Theory Elementary_Normed_Spaces
section ‹Elementary Normed Vector Spaces›
theory Elementary_Normed_Spaces
imports
"HOL-Library.FuncSet"
Elementary_Metric_Spaces Cartesian_Space
Connected
begin
subsection ‹Orthogonal Transformation of Balls›
subsection ‹Various Lemmas Combining Imports›
lemma open_sums:
fixes T :: "('b::real_normed_vector) set"
assumes "open S ∨ open T"
shows "open (⋃x∈ S. ⋃y ∈ T. {x + y})"
using assms
proof
assume S: "open S"
show ?thesis
proof (clarsimp simp: open_dist)
fix x y
assume "x ∈ S" "y ∈ T"
with S obtain e where "e > 0" and e: "⋀x'. dist x' x < e ⟹ x' ∈ S"
by (auto simp: open_dist)
then have "⋀z. dist z (x + y) < e ⟹ ∃x∈S. ∃y∈T. z = x + y"
by (metis ‹y ∈ T› diff_add_cancel dist_add_cancel2)
then show "∃e>0. ∀z. dist z (x + y) < e ⟶ (∃x∈S. ∃y∈T. z = x + y)"
using ‹0 < e› ‹x ∈ S› by blast
qed
next
assume T: "open T"
show ?thesis
proof (clarsimp simp: open_dist)
fix x y
assume "x ∈ S" "y ∈ T"
with T obtain e where "e > 0" and e: "⋀x'. dist x' y < e ⟹ x' ∈ T"
by (auto simp: open_dist)
then have "⋀z. dist z (x + y) < e ⟹ ∃x∈S. ∃y∈T. z = x + y"
by (metis ‹x ∈ S› add_diff_cancel_left' add_diff_eq diff_diff_add dist_norm)
then show "∃e>0. ∀z. dist z (x + y) < e ⟶ (∃x∈S. ∃y∈T. z = x + y)"
using ‹0 < e› ‹y ∈ T› by blast
qed
qed
lemma image_orthogonal_transformation_ball:
fixes f :: "'a::euclidean_space ⇒ 'a"
assumes "orthogonal_transformation f"
shows "f ` ball x r = ball (f x) r"
proof (intro equalityI subsetI)
fix y assume "y ∈ f ` ball x r"
with assms show "y ∈ ball (f x) r"
by (auto simp: orthogonal_transformation_isometry)
next
fix y assume y: "y ∈ ball (f x) r"
then obtain z where z: "y = f z"
using assms orthogonal_transformation_surj by blast
with y assms show "y ∈ f ` ball x r"
by (auto simp: orthogonal_transformation_isometry)
qed
lemma image_orthogonal_transformation_cball:
fixes f :: "'a::euclidean_space ⇒ 'a"
assumes "orthogonal_transformation f"
shows "f ` cball x r = cball (f x) r"
proof (intro equalityI subsetI)
fix y assume "y ∈ f ` cball x r"
with assms show "y ∈ cball (f x) r"
by (auto simp: orthogonal_transformation_isometry)
next
fix y assume y: "y ∈ cball (f x) r"
then obtain z where z: "y = f z"
using assms orthogonal_transformation_surj by blast
with y assms show "y ∈ f ` cball x r"
by (auto simp: orthogonal_transformation_isometry)
qed
subsection ‹Support›
definition (in monoid_add) support_on :: "'b set ⇒ ('b ⇒ 'a) ⇒ 'b set"
where "support_on S f = {x∈S. f x ≠ 0}"
lemma in_support_on: "x ∈ support_on S f ⟷ x ∈ S ∧ f x ≠ 0"
by (simp add: support_on_def)
lemma support_on_simps[simp]:
"support_on {} f = {}"
"support_on (insert x S) f =
(if f x = 0 then support_on S f else insert x (support_on S f))"
"support_on (S ∪ T) f = support_on S f ∪ support_on T f"
"support_on (S ∩ T) f = support_on S f ∩ support_on T f"
"support_on (S - T) f = support_on S f - support_on T f"
"support_on (f ` S) g = f ` (support_on S (g ∘ f))"
unfolding support_on_def by auto
lemma support_on_cong:
"(⋀x. x ∈ S ⟹ f x = 0 ⟷ g x = 0) ⟹ support_on S f = support_on S g"
by (auto simp: support_on_def)
lemma support_on_if: "a ≠ 0 ⟹ support_on A (λx. if P x then a else 0) = {x∈A. P x}"
by (auto simp: support_on_def)
lemma support_on_if_subset: "support_on A (λx. if P x then a else 0) ⊆ {x ∈ A. P x}"
by (auto simp: support_on_def)
lemma finite_support[intro]: "finite S ⟹ finite (support_on S f)"
unfolding support_on_def by auto
definition (in comm_monoid_add) supp_sum :: "('b ⇒ 'a) ⇒ 'b set ⇒ 'a"
where "supp_sum f S = (∑x∈support_on S f. f x)"
lemma supp_sum_empty[simp]: "supp_sum f {} = 0"
unfolding supp_sum_def by auto
lemma supp_sum_insert[simp]:
"finite (support_on S f) ⟹
supp_sum f (insert x S) = (if x ∈ S then supp_sum f S else f x + supp_sum f S)"
by (simp add: supp_sum_def in_support_on insert_absorb)
lemma supp_sum_divide_distrib: "supp_sum f A / (r::'a::field) = supp_sum (λn. f n / r) A"
by (cases "r = 0")
(auto simp: supp_sum_def sum_divide_distrib intro!: sum.cong support_on_cong)
subsection ‹Intervals›
lemma image_affinity_interval:
fixes c :: "'a::ordered_real_vector"
shows "((λx. m *⇩R x + c) ` {a..b}) =
(if {a..b}={} then {}
else if 0 ≤ m then {m *⇩R a + c .. m *⇩R b + c}
else {m *⇩R b + c .. m *⇩R a + c})"
(is "?lhs = ?rhs")
proof (cases "m=0")
case True
then show ?thesis
by force
next
case False
show ?thesis
proof
show "?lhs ⊆ ?rhs"
by (auto simp: scaleR_left_mono scaleR_left_mono_neg)
show "?rhs ⊆ ?lhs"
proof (clarsimp, intro conjI impI subsetI)
show "⟦0 ≤ m; a ≤ b; x ∈ {m *⇩R a + c..m *⇩R b + c}⟧
⟹ x ∈ (λx. m *⇩R x + c) ` {a..b}" for x
using False
by (rule_tac x="inverse m *⇩R (x-c)" in image_eqI)
(auto simp: pos_le_divideR_eq pos_divideR_le_eq le_diff_eq diff_le_eq)
show "⟦¬ 0 ≤ m; a ≤ b; x ∈ {m *⇩R b + c..m *⇩R a + c}⟧
⟹ x ∈ (λx. m *⇩R x + c) ` {a..b}" for x
by (rule_tac x="inverse m *⇩R (x-c)" in image_eqI)
(auto simp add: neg_le_divideR_eq neg_divideR_le_eq le_diff_eq diff_le_eq)
qed
qed
qed
subsection ‹Limit Points›
lemma islimpt_ball:
fixes x y :: "'a::{real_normed_vector,perfect_space}"
shows "y islimpt ball x e ⟷ 0 < e ∧ y ∈ cball x e"
(is "?lhs ⟷ ?rhs")
proof
show ?rhs if ?lhs
proof
{
assume "e ≤ 0"
then have *: "ball x e = {}"
using ball_eq_empty[of x e] by auto
have False using ‹?lhs›
unfolding * using islimpt_EMPTY[of y] by auto
}
then show "e > 0" by (metis not_less)
show "y ∈ cball x e"
using closed_cball[of x e] islimpt_subset[of y "ball x e" "cball x e"]
ball_subset_cball[of x e] ‹?lhs›
unfolding closed_limpt by auto
qed
show ?lhs if ?rhs
proof -
from that have "e > 0" by auto
{
fix d :: real
assume "d > 0"
have "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d"
proof (cases "d ≤ dist x y")
case True
then show ?thesis
proof (cases "x = y")
case True
then have False
using ‹d ≤ dist x y› ‹d>0› by auto
then show ?thesis
by auto
next
case False
have "dist x (y - (d / (2 * dist y x)) *⇩R (y - x)) =
norm (x - y + (d / (2 * norm (y - x))) *⇩R (y - x))"
unfolding mem_cball mem_ball dist_norm diff_diff_eq2 diff_add_eq[symmetric]
by auto
also have "… = ¦- 1 + d / (2 * norm (x - y))¦ * norm (x - y)"
using scaleR_left_distrib[of "- 1" "d / (2 * norm (y - x))", symmetric, of "y - x"]
unfolding scaleR_minus_left scaleR_one
by (auto simp: norm_minus_commute)
also have "… = ¦- norm (x - y) + d / 2¦"
unfolding abs_mult_pos[of "norm (x - y)", OF norm_ge_zero[of "x - y"]]
unfolding distrib_right using ‹x≠y› by auto
also have "… ≤ e - d/2" using ‹d ≤ dist x y› and ‹d>0› and ‹?rhs›
by (auto simp: dist_norm)
finally have "y - (d / (2 * dist y x)) *⇩R (y - x) ∈ ball x e" using ‹d>0›
by auto
moreover
have "(d / (2*dist y x)) *⇩R (y - x) ≠ 0"
using ‹x≠y›[unfolded dist_nz] ‹d>0› unfolding scaleR_eq_0_iff
by (auto simp: dist_commute)
moreover
have "dist (y - (d / (2 * dist y x)) *⇩R (y - x)) y < d"
using ‹0 < d› by (fastforce simp: dist_norm)
ultimately show ?thesis
by (rule_tac x = "y - (d / (2*dist y x)) *⇩R (y - x)" in bexI) auto
qed
next
case False
then have "d > dist x y" by auto
show "∃x' ∈ ball x e. x' ≠ y ∧ dist x' y < d"
proof (cases "x = y")
case True
obtain z where z: "z ≠ y" "dist z y < min e d"
using perfect_choose_dist[of "min e d" y]
using ‹d > 0› ‹e>0› by auto
show ?thesis
by (metis True z dist_commute mem_ball min_less_iff_conj)
next
case False
then show ?thesis
using ‹d>0› ‹d > dist x y› ‹?rhs› by force
qed
qed
}
then show ?thesis
unfolding mem_cball islimpt_approachable mem_ball by auto
qed
qed
lemma closure_ball_lemma:
fixes x y :: "'a::real_normed_vector"
assumes "x ≠ y"
shows "y islimpt ball x (dist x y)"
proof (rule islimptI)
fix T
assume "y ∈ T" "open T"
then obtain r where "0 < r" "∀z. dist z y < r ⟶ z ∈ T"
unfolding open_dist by fast
define k where "k = min 1 (r / (2 * dist x y))"
define z where "z = y + scaleR k (x - y)"
have z_def2: "z = x + scaleR (1 - k) (y - x)"
unfolding z_def by (simp add: algebra_simps)
have "dist z y < r"
unfolding z_def k_def using ‹0 < r›
by (simp add: dist_norm min_def)
then have "z ∈ T"
using ‹∀z. dist z y < r ⟶ z ∈ T› by simp
have "dist x z < dist x y"
using ‹0 < r› assms by (simp add: z_def2 k_def dist_norm norm_minus_commute)
then have "z ∈ ball x (dist x y)"
by simp
have "z ≠ y"
unfolding z_def k_def using ‹x ≠ y› ‹0 < r›
by (simp add: min_def)
show "∃z∈ball x (dist x y). z ∈ T ∧ z ≠ y"
using ‹z ∈ ball x (dist x y)› ‹z ∈ T› ‹z ≠ y›
by fast
qed
subsection ‹Balls and Spheres in Normed Spaces›
lemma mem_ball_0 [simp]: "x ∈ ball 0 e ⟷ norm x < e"
for x :: "'a::real_normed_vector"
by simp
lemma mem_cball_0 [simp]: "x ∈ cball 0 e ⟷ norm x ≤ e"
for x :: "'a::real_normed_vector"
by simp
lemma closure_ball [simp]:
fixes x :: "'a::real_normed_vector"
assumes "0 < e"
shows "closure (ball x e) = cball x e"
proof
show "closure (ball x e) ⊆ cball x e"
using closed_cball closure_minimal by blast
have "⋀y. dist x y < e ∨ dist x y = e ⟹ y ∈ closure (ball x e)"
by (metis Un_iff assms closure_ball_lemma closure_def dist_eq_0_iff mem_Collect_eq mem_ball)
then show "cball x e ⊆ closure (ball x e)"
by force
qed
lemma mem_sphere_0 [simp]: "x ∈ sphere 0 e ⟷ norm x = e"
for x :: "'a::real_normed_vector"
by simp
lemma interior_cball [simp]:
fixes x :: "'a::{real_normed_vector, perfect_space}"
shows "interior (cball x e) = ball x e"
proof (cases "e ≥ 0")
case False note cs = this
from cs have null: "ball x e = {}"
using ball_empty[of e x] by auto
moreover
have "cball x e = {}"
proof (rule equals0I)
fix y
assume "y ∈ cball x e"
then show False
by (metis ball_eq_empty null cs dist_eq_0_iff dist_le_zero_iff empty_subsetI mem_cball
subset_antisym subset_ball)
qed
then have "interior (cball x e) = {}"
using interior_empty by auto
ultimately show ?thesis by blast
next
case True note cs = this
have "ball x e ⊆ cball x e"
using ball_subset_cball by auto
moreover
{
fix S y
assume as: "S ⊆ cball x e" "open S" "y∈S"
then obtain d where "d>0" and d: "∀x'. dist x' y < d ⟶ x' ∈ S"
unfolding open_dist by blast
then obtain xa where xa_y: "xa ≠ y" and xa: "dist xa y < d"
using perfect_choose_dist [of d] by auto
have "xa ∈ S"
using d[THEN spec[where x = xa]]
using xa by (auto simp: dist_commute)
then have xa_cball: "xa ∈ cball x e"
using as(1) by auto
then have "y ∈ ball x e"
proof (cases "x = y")
case True
then have "e > 0" using cs order.order_iff_strict xa_cball xa_y by fastforce
then show "y ∈ ball x e"
using ‹x = y › by simp
next
case False
have "dist (y + (d / 2 / dist y x) *⇩R (y - x)) y < d"
unfolding dist_norm
using ‹d>0› norm_ge_zero[of "y - x"] ‹x ≠ y› by auto
then have *: "y + (d / 2 / dist y x) *⇩R (y - x) ∈ cball x e"
using d as(1)[unfolded subset_eq] by blast
have "y - x ≠ 0" using ‹x ≠ y› by auto
hence **:"d / (2 * norm (y - x)) > 0"
unfolding zero_less_norm_iff[symmetric] using ‹d>0› by auto
have "dist (y + (d / 2 / dist y x) *⇩R (y - x)) x =
norm (y + (d / (2 * norm (y - x))) *⇩R y - (d / (2 * norm (y - x))) *⇩R x - x)"
by (auto simp: dist_norm algebra_simps)
also have "… = norm ((1 + d / (2 * norm (y - x))) *⇩R (y - x))"
by (auto simp: algebra_simps)
also have "… = ¦1 + d / (2 * norm (y - x))¦ * norm (y - x)"
using ** by auto
also have "… = (dist y x) + d/2"
using ** by (auto simp: distrib_right dist_norm)
finally have "e ≥ dist x y +d/2"
using *[unfolded mem_cball] by (auto simp: dist_commute)
then show "y ∈ ball x e"
unfolding mem_ball using ‹d>0› by auto
qed
}
then have "∀S ⊆ cball x e. open S ⟶ S ⊆ ball x e"
by auto
ultimately show ?thesis
using interior_unique[of "ball x e" "cball x e"]
using open_ball[of x e]
by auto
qed
lemma frontier_ball [simp]:
fixes a :: "'a::real_normed_vector"
shows "0 < e ⟹ frontier (ball a e) = sphere a e"
by (force simp: frontier_def)
lemma frontier_cball [simp]:
fixes a :: "'a::{real_normed_vector, perfect_space}"
shows "frontier (cball a e) = sphere a e"
by (force simp: frontier_def)
corollary compact_sphere [simp]:
fixes a :: "'a::{real_normed_vector,perfect_space,heine_borel}"
shows "compact (sphere a r)"
using compact_frontier [of "cball a r"] by simp
corollary bounded_sphere [simp]:
fixes a :: "'a::{real_normed_vector,perfect_space,heine_borel}"
shows "bounded (sphere a r)"
by (simp add: compact_imp_bounded)
corollary closed_sphere [simp]:
fixes a :: "'a::{real_normed_vector,perfect_space,heine_borel}"
shows "closed (sphere a r)"
by (simp add: compact_imp_closed)
lemma image_add_ball [simp]:
fixes a :: "'a::real_normed_vector"
shows "(+) b ` ball a r = ball (a+b) r"
proof -
{ fix x :: 'a
assume "dist (a + b) x < r"
moreover
have "b + (x - b) = x"
by simp
ultimately have "x ∈ (+) b ` ball a r"
by (metis add.commute dist_add_cancel image_eqI mem_ball) }
then show ?thesis
by (auto simp: add.commute)
qed
lemma image_add_cball [simp]:
fixes a :: "'a::real_normed_vector"
shows "(+) b ` cball a r = cball (a+b) r"
proof -
have "⋀x. dist (a + b) x ≤ r ⟹ ∃y∈cball a r. x = b + y"
by (metis (no_types) add.commute diff_add_cancel dist_add_cancel2 mem_cball)
then show ?thesis
by (force simp: add.commute)
qed
subsection ‹Various Lemmas on Normed Algebras›
lemma closed_of_nat_image: "closed (of_nat ` A :: 'a::real_normed_algebra_1 set)"
by (rule discrete_imp_closed[of 1]) (auto simp: dist_of_nat)
lemma closed_of_int_image: "closed (of_int ` A :: 'a::real_normed_algebra_1 set)"
by (rule discrete_imp_closed[of 1]) (auto simp: dist_of_int)
lemma closed_Nats [simp]: "closed (ℕ :: 'a :: real_normed_algebra_1 set)"
unfolding Nats_def by (rule closed_of_nat_image)
lemma closed_Ints [simp]: "closed (ℤ :: 'a :: real_normed_algebra_1 set)"
unfolding Ints_def by (rule closed_of_int_image)
lemma closed_subset_Ints:
fixes A :: "'a :: real_normed_algebra_1 set"
assumes "A ⊆ ℤ"
shows "closed A"
proof (intro discrete_imp_closed[OF zero_less_one] ballI impI, goal_cases)
case (1 x y)
with assms have "x ∈ ℤ" and "y ∈ ℤ" by auto
with ‹dist y x < 1› show "y = x"
by (auto elim!: Ints_cases simp: dist_of_int)
qed
subsection ‹Filters›
definition indirection :: "'a::real_normed_vector ⇒ 'a ⇒ 'a filter" (infixr ‹indirection› 70)
where "a indirection v = at a within {b. ∃c≥0. b - a = scaleR c v}"
subsection ‹Trivial Limits›
lemma trivial_limit_at_infinity:
"¬ trivial_limit (at_infinity :: ('a::{real_normed_vector,perfect_space}) filter)"
proof -
obtain x::'a where "x ≠ 0"
by (meson perfect_choose_dist zero_less_one)
then have "b ≤ norm ((b / norm x) *⇩R x)" for b
by simp
then show ?thesis
unfolding trivial_limit_def eventually_at_infinity
by blast
qed
lemma at_within_ball_bot_iff:
fixes x y :: "'a::{real_normed_vector,perfect_space}"
shows "at x within ball y r = bot ⟷ (r=0 ∨ x ∉ cball y r)"
unfolding trivial_limit_within
by (metis (no_types) cball_empty equals0D islimpt_ball less_linear)
subsection ‹Limits›
proposition Lim_at_infinity: "(f ⤏ l) at_infinity ⟷ (∀e>0. ∃b. ∀x. norm x ≥ b ⟶ dist (f x) l < e)"
by (auto simp: tendsto_iff eventually_at_infinity)
corollary Lim_at_infinityI [intro?]:
assumes "⋀e. e > 0 ⟹ ∃B. ∀x. norm x ≥ B ⟶ dist (f x) l ≤ e"
shows "(f ⤏ l) at_infinity"
proof -
have "⋀e. e > 0 ⟹ ∃B. ∀x. norm x ≥ B ⟶ dist (f x) l < e"
by (meson assms dense le_less_trans)
then show ?thesis
using Lim_at_infinity by blast
qed
lemma Lim_transform_within_set_eq:
fixes a :: "'a::metric_space" and l :: "'b::metric_space"
shows "eventually (λx. x ∈ S ⟷ x ∈ T) (at a)
⟹ ((f ⤏ l) (at a within S) ⟷ (f ⤏ l) (at a within T))"
by (force intro: Lim_transform_within_set elim: eventually_mono)
lemma Lim_null:
fixes f :: "'a ⇒ 'b::real_normed_vector"
shows "(f ⤏ l) net ⟷ ((λx. f(x) - l) ⤏ 0) net"
by (simp add: Lim dist_norm)
lemma Lim_null_comparison:
fixes f :: "'a ⇒ 'b::real_normed_vector"
assumes "eventually (λx. norm (f x) ≤ g x) net" "(g ⤏ 0) net"
shows "(f ⤏ 0) net"
using assms(2)
proof (rule metric_tendsto_imp_tendsto)
show "eventually (λx. dist (f x) 0 ≤ dist (g x) 0) net"
using assms(1) by (rule eventually_mono) (simp add: dist_norm)
qed
lemma Lim_transform_bound:
fixes f :: "'a ⇒ 'b::real_normed_vector"
and g :: "'a ⇒ 'c::real_normed_vector"
assumes "eventually (λn. norm (f n) ≤ norm (g n)) net"
and "(g ⤏ 0) net"
shows "(f ⤏ 0) net"
using assms(1) tendsto_norm_zero [OF assms(2)]
by (rule Lim_null_comparison)
lemma lim_null_mult_right_bounded:
fixes f :: "'a ⇒ 'b::real_normed_div_algebra"
assumes f: "(f ⤏ 0) F" and g: "eventually (λx. norm(g x) ≤ B) F"
shows "((λz. f z * g z) ⤏ 0) F"
proof -
have "((λx. norm (f x) * norm (g x)) ⤏ 0) F"
proof (rule Lim_null_comparison)
show "∀⇩F x in F. norm (norm (f x) * norm (g x)) ≤ norm (f x) * B"
by (simp add: eventually_mono [OF g] mult_left_mono)
show "((λx. norm (f x) * B) ⤏ 0) F"
by (simp add: f tendsto_mult_left_zero tendsto_norm_zero)
qed
then show ?thesis
by (subst tendsto_norm_zero_iff [symmetric]) (simp add: norm_mult)
qed
lemma lim_null_mult_left_bounded:
fixes f :: "'a ⇒ 'b::real_normed_div_algebra"
assumes g: "eventually (λx. norm(g x) ≤ B) F" and f: "(f ⤏ 0) F"
shows "((λz. g z * f z) ⤏ 0) F"
proof -
have "((λx. norm (g x) * norm (f x)) ⤏ 0) F"
proof (rule Lim_null_comparison)
show "∀⇩F x in F. norm (norm (g x) * norm (f x)) ≤ B * norm (f x)"
by (simp add: eventually_mono [OF g] mult_right_mono)
show "((λx. B * norm (f x)) ⤏ 0) F"
by (simp add: f tendsto_mult_right_zero tendsto_norm_zero)
qed
then show ?thesis
by (subst tendsto_norm_zero_iff [symmetric]) (simp add: norm_mult)
qed
lemma lim_null_scaleR_bounded:
assumes f: "(f ⤏ 0) net" and gB: "eventually (λa. f a = 0 ∨ norm(g a) ≤ B) net"
shows "((λn. f n *⇩R g n) ⤏ 0) net"
proof
fix ε::real
assume "0 < ε"
then have B: "0 < ε / (abs B + 1)" by simp
have *: "¦f x¦ * norm (g x) < ε" if f: "¦f x¦ * (¦B¦ + 1) < ε" and g: "norm (g x) ≤ B" for x
proof -
have "¦f x¦ * norm (g x) ≤ ¦f x¦ * B"
by (simp add: mult_left_mono g)
also have "… ≤ ¦f x¦ * (¦B¦ + 1)"
by (simp add: mult_left_mono)
also have "… < ε"
by (rule f)
finally show ?thesis .
qed
have "⋀x. ⟦¦f x¦ < ε / (¦B¦ + 1); norm (g x) ≤ B⟧ ⟹ ¦f x¦ * norm (g x) < ε"
by (simp add: "*" pos_less_divide_eq)
then show "∀⇩F x in net. dist (f x *⇩R g x) 0 < ε"
using ‹0 < ε› by (auto intro: eventually_mono [OF eventually_conj [OF tendstoD [OF f B] gB]])
qed
lemma Lim_norm_ubound:
fixes f :: "'a ⇒ 'b::real_normed_vector"
assumes "¬(trivial_limit net)" "(f ⤏ l) net" "eventually (λx. norm(f x) ≤ e) net"
shows "norm(l) ≤ e"
using assms by (fast intro: tendsto_le tendsto_intros)
lemma Lim_norm_lbound:
fixes f :: "'a ⇒ 'b::real_normed_vector"
assumes "¬ trivial_limit net"
and "(f ⤏ l) net"
and "eventually (λx. e ≤ norm (f x)) net"
shows "e ≤ norm l"
using assms by (fast intro: tendsto_le tendsto_intros)
text‹Limit under bilinear function›
lemma Lim_bilinear:
assumes "(f ⤏ l) net"
and "(g ⤏ m) net"
and "bounded_bilinear h"
shows "((λx. h (f x) (g x)) ⤏ (h l m)) net"
using ‹bounded_bilinear h› ‹(f ⤏ l) net› ‹(g ⤏ m) net›
by (rule bounded_bilinear.tendsto)
lemma Lim_at_zero:
fixes a :: "'a::real_normed_vector"
and l :: "'b::topological_space"
shows "(f ⤏ l) (at a) ⟷ ((λx. f(a + x)) ⤏ l) (at 0)"
using LIM_offset_zero LIM_offset_zero_cancel ..
subsection ‹Limit Point of Filter›
lemma netlimit_at_vector:
fixes a :: "'a::real_normed_vector"
shows "netlimit (at a) = a"
proof (cases "∃x. x ≠ a")
case True then obtain x where x: "x ≠ a" ..
have "⋀d. 0 < d ⟹ ∃x. x ≠ a ∧ norm (x - a) < d"
by (rule_tac x="a + scaleR (d / 2) (sgn (x - a))" in exI) (simp add: norm_sgn sgn_zero_iff x)
then have "¬ trivial_limit (at a)"
by (auto simp: trivial_limit_def eventually_at dist_norm)
then show ?thesis
by (rule Lim_ident_at [of a UNIV])
qed simp
subsection ‹Boundedness›
lemma continuous_on_closure_norm_le:
fixes f :: "'a::metric_space ⇒ 'b::real_normed_vector"
assumes "continuous_on (closure s) f"
and "∀y ∈ s. norm(f y) ≤ b"
and "x ∈ (closure s)"
shows "norm (f x) ≤ b"
proof -
have *: "f ` s ⊆ cball 0 b"
using assms(2)[unfolded mem_cball_0[symmetric]] by auto
show ?thesis
by (meson "*" assms(1) assms(3) closed_cball image_closure_subset image_subset_iff mem_cball_0)
qed
lemma bounded_pos: "bounded S ⟷ (∃b>0. ∀x∈ S. norm x ≤ b)"
unfolding bounded_iff
by (meson less_imp_le not_le order_trans zero_less_one)
lemma bounded_pos_less: "bounded S ⟷ (∃b>0. ∀x∈ S. norm x < b)"
by (metis bounded_pos le_less_trans less_imp_le linordered_field_no_ub)
lemma bounded_normE:
assumes "bounded A"
obtains B where "B > 0" "⋀z. z ∈ A ⟹ norm z ≤ B"
by (meson assms bounded_pos)
lemma bounded_normE_less:
assumes "bounded A"
obtains B where "B > 0" "⋀z. z ∈ A ⟹ norm z < B"
by (meson assms bounded_pos_less)
lemma Bseq_eq_bounded:
fixes f :: "nat ⇒ 'a::real_normed_vector"
shows "Bseq f ⟷ bounded (range f)"
unfolding Bseq_def bounded_pos by auto
lemma bounded_linear_image:
assumes "bounded S"
and "bounded_linear f"
shows "bounded (f ` S)"
proof -
from assms(1) obtain b where "b > 0" and b: "∀x∈S. norm x ≤ b"
unfolding bounded_pos by auto
from assms(2) obtain B where B: "B > 0" "∀x. norm (f x) ≤ B * norm x"
using bounded_linear.pos_bounded by (auto simp: ac_simps)
show ?thesis
unfolding bounded_pos
proof (intro exI, safe)
show "norm (f x) ≤ B * b" if "x ∈ S" for x
by (meson B b less_imp_le mult_left_mono order_trans that)
qed (use ‹b > 0› ‹B > 0› in auto)
qed
lemma bounded_scaling:
fixes S :: "'a::real_normed_vector set"
shows "bounded S ⟹ bounded ((λx. c *⇩R x) ` S)"
by (simp add: bounded_linear_image bounded_linear_scaleR_right)
lemma bounded_scaleR_comp:
fixes f :: "'a ⇒ 'b::real_normed_vector"
assumes "bounded (f ` S)"
shows "bounded ((λx. r *⇩R f x) ` S)"
using bounded_scaling[of "f ` S" r] assms
by (auto simp: image_image)
lemma bounded_translation:
fixes S :: "'a::real_normed_vector set"
assumes "bounded S"
shows "bounded ((λx. a + x) ` S)"
proof -
from assms obtain b where b: "b > 0" "∀x∈S. norm x ≤ b"
unfolding bounded_pos by auto
{
fix x
assume "x ∈ S"
then have "norm (a + x) ≤ b + norm a"
using norm_triangle_ineq[of a x] b by auto
}
then show ?thesis
unfolding bounded_pos
using norm_ge_zero[of a] b(1) and add_strict_increasing[of b 0 "norm a"]
by (auto intro!: exI[of _ "b + norm a"])
qed
lemma bounded_translation_minus:
fixes S :: "'a::real_normed_vector set"
shows "bounded S ⟹ bounded ((λx. x - a) ` S)"
using bounded_translation [of S "-a"] by simp
lemma bounded_uminus [simp]:
fixes X :: "'a::real_normed_vector set"
shows "bounded (uminus ` X) ⟷ bounded X"
by (auto simp: bounded_def dist_norm; rule_tac x="-x" in exI; force simp: add.commute norm_minus_commute)
lemma uminus_bounded_comp [simp]:
fixes f :: "'a ⇒ 'b::real_normed_vector"
shows "bounded ((λx. - f x) ` S) ⟷ bounded (f ` S)"
using bounded_uminus[of "f ` S"]
by (auto simp: image_image)
lemma bounded_plus_comp:
fixes f g::"'a ⇒ 'b::real_normed_vector"
assumes "bounded (f ` S)"
assumes "bounded (g ` S)"
shows "bounded ((λx. f x + g x) ` S)"
proof -
{
fix B C
assume "⋀x. x∈S ⟹ norm (f x) ≤ B" "⋀x. x∈S ⟹ norm (g x) ≤ C"
then have "⋀x. x ∈ S ⟹ norm (f x + g x) ≤ B + C"
by (auto intro!: norm_triangle_le add_mono)
} then show ?thesis
using assms by (fastforce simp: bounded_iff)
qed
lemma bounded_plus:
fixes S ::"'a::real_normed_vector set"
assumes "bounded S" "bounded T"
shows "bounded ((λ(x,y). x + y) ` (S × T))"
using bounded_plus_comp [of fst "S × T" snd] assms
by (auto simp: split_def split: if_split_asm)
lemma bounded_minus_comp:
"bounded (f ` S) ⟹ bounded (g ` S) ⟹ bounded ((λx. f x - g x) ` S)"
for f g::"'a ⇒ 'b::real_normed_vector"
using bounded_plus_comp[of "f" S "λx. - g x"]
by auto
lemma bounded_minus:
fixes S ::"'a::real_normed_vector set"
assumes "bounded S" "bounded T"
shows "bounded ((λ(x,y). x - y) ` (S × T))"
using bounded_minus_comp [of fst "S × T" snd] assms
by (auto simp: split_def split: if_split_asm)
lemma bounded_sums:
fixes S :: "'a::real_normed_vector set"
assumes "bounded S" and "bounded T"
shows "bounded (⋃x∈ S. ⋃y ∈ T. {x + y})"
using assms by (simp add: bounded_iff) (meson norm_triangle_mono)
lemma bounded_differences:
fixes S :: "'a::real_normed_vector set"
assumes "bounded S" and "bounded T"
shows "bounded (⋃x∈ S. ⋃y ∈ T. {x - y})"
using assms by (simp add: bounded_iff) (meson add_mono norm_triangle_le_diff)
lemma not_bounded_UNIV[simp]:
"¬ bounded (UNIV :: 'a::{real_normed_vector, perfect_space} set)"
proof (auto simp: bounded_pos not_le)
obtain x :: 'a where "x ≠ 0"
using perfect_choose_dist [OF zero_less_one] by fast
fix b :: real
assume b: "b >0"
have b1: "b +1 ≥ 0"
using b by simp
with ‹x ≠ 0› have "b < norm (scaleR (b + 1) (sgn x))"
by (simp add: norm_sgn)
then show "∃x::'a. b < norm x" ..
qed
corollary cobounded_imp_unbounded:
fixes S :: "'a::{real_normed_vector, perfect_space} set"
shows "bounded (- S) ⟹ ¬ bounded S"
using bounded_Un [of S "-S"] by (simp)
subsection‹Relations among convergence and absolute convergence for power series›
lemma summable_imp_bounded:
fixes f :: "nat ⇒ 'a::real_normed_vector"
shows "summable f ⟹ bounded (range f)"
by (frule summable_LIMSEQ_zero) (simp add: convergent_imp_bounded)
lemma summable_imp_sums_bounded:
"summable f ⟹ bounded (range (λn. sum f {..<n}))"
by (auto simp: summable_def sums_def dest: convergent_imp_bounded)
lemma power_series_conv_imp_absconv_weak:
fixes a:: "nat ⇒ 'a::{real_normed_div_algebra,banach}" and w :: 'a
assumes sum: "summable (λn. a n * z ^ n)" and no: "norm w < norm z"
shows "summable (λn. of_real(norm(a n)) * w ^ n)"
proof -
obtain M where M: "⋀x. norm (a x * z ^ x) ≤ M"
using summable_imp_bounded [OF sum] by (force simp: bounded_iff)
show ?thesis
proof (rule series_comparison_complex)
have "⋀n. norm (a n) * norm z ^ n ≤ M"
by (metis (no_types) M norm_mult norm_power)
then show "summable (λn. complex_of_real (norm (a n) * norm w ^ n))"
using Abel_lemma no norm_ge_zero summable_of_real by blast
qed (auto simp: norm_mult norm_power)
qed
subsection ‹Normed spaces with the Heine-Borel property›
lemma not_compact_UNIV[simp]:
fixes s :: "'a::{real_normed_vector,perfect_space,heine_borel} set"
shows "¬ compact (UNIV::'a set)"
by (simp add: compact_eq_bounded_closed)
lemma not_compact_space_euclideanreal [simp]: "¬ compact_space euclideanreal"
by (simp add: compact_space_def)
text‹Representing sets as the union of a chain of compact sets.›
lemma closed_Union_compact_subsets:
fixes S :: "'a::{heine_borel,real_normed_vector} set"
assumes "closed S"
obtains F where "⋀n. compact(F n)" "⋀n. F n ⊆ S" "⋀n. F n ⊆ F(Suc n)"
"(⋃n. F n) = S" "⋀K. ⟦compact K; K ⊆ S⟧ ⟹ ∃N. ∀n ≥ N. K ⊆ F n"
proof
show "compact (S ∩ cball 0 (of_nat n))" for n
using assms compact_eq_bounded_closed by auto
next
show "(⋃n. S ∩ cball 0 (real n)) = S"
by (auto simp: real_arch_simple)
next
fix K :: "'a set"
assume "compact K" "K ⊆ S"
then obtain N where "K ⊆ cball 0 N"
by (meson bounded_pos mem_cball_0 compact_imp_bounded subsetI)
then show "∃N. ∀n≥N. K ⊆ S ∩ cball 0 (real n)"
by (metis of_nat_le_iff Int_subset_iff ‹K ⊆ S› real_arch_simple subset_cball subset_trans)
qed auto
subsection ‹Intersecting chains of compact sets and the Baire property›
proposition bounded_closed_chain:
fixes ℱ :: "'a::heine_borel set set"
assumes "B ∈ ℱ" "bounded B" and ℱ: "⋀S. S ∈ ℱ ⟹ closed S" and "{} ∉ ℱ"
and chain: "⋀S T. S ∈ ℱ ∧ T ∈ ℱ ⟹ S ⊆ T ∨ T ⊆ S"
shows "⋂ℱ ≠ {}"
proof -
have "B ∩ ⋂ℱ ≠ {}"
proof (rule compact_imp_fip)
show "compact B" "⋀T. T ∈ ℱ ⟹ closed T"
by (simp_all add: assms compact_eq_bounded_closed)
show "⟦finite 𝒢; 𝒢 ⊆ ℱ⟧ ⟹ B ∩ ⋂𝒢 ≠ {}" for 𝒢
proof (induction 𝒢 rule: finite_induct)
case empty
with assms show ?case by force
next
case (insert U 𝒢)
then have "U ∈ ℱ" and ne: "B ∩ ⋂𝒢 ≠ {}" by auto
then consider "B ⊆ U" | "U ⊆ B"
using ‹B ∈ ℱ› chain by blast
then show ?case
proof cases
case 1
then show ?thesis
using Int_left_commute ne by auto
next
case 2
have "U ≠ {}"
using ‹U ∈ ℱ› ‹{} ∉ ℱ› by blast
moreover
have False if "⋀x. x ∈ U ⟹ ∃Y∈𝒢. x ∉ Y"
proof -
have "⋀x. x ∈ U ⟹ ∃Y∈𝒢. Y ⊆ U"
by (metis chain contra_subsetD insert.prems insert_subset that)
then obtain Y where "Y ∈ 𝒢" "Y ⊆ U"
by (metis all_not_in_conv ‹U ≠ {}›)
moreover obtain x where "x ∈ ⋂𝒢"
by (metis Int_emptyI ne)
ultimately show ?thesis
by (metis Inf_lower subset_eq that)
qed
with 2 show ?thesis
by blast
qed
qed
qed
then show ?thesis by blast
qed
corollary compact_chain:
fixes ℱ :: "'a::heine_borel set set"
assumes "⋀S. S ∈ ℱ ⟹ compact S" "{} ∉ ℱ"
"⋀S T. S ∈ ℱ ∧ T ∈ ℱ ⟹ S ⊆ T ∨ T ⊆ S"
shows "⋂ ℱ ≠ {}"
proof (cases "ℱ = {}")
case True
then show ?thesis by auto
next
case False
show ?thesis
by (metis False all_not_in_conv assms compact_imp_bounded compact_imp_closed bounded_closed_chain)
qed
lemma compact_nest:
fixes F :: "'a::linorder ⇒ 'b::heine_borel set"
assumes F: "⋀n. compact(F n)" "⋀n. F n ≠ {}" and mono: "⋀m n. m ≤ n ⟹ F n ⊆ F m"
shows "⋂(range F) ≠ {}"
proof -
have *: "⋀S T. S ∈ range F ∧ T ∈ range F ⟹ S ⊆ T ∨ T ⊆ S"
by (metis mono image_iff le_cases)
show ?thesis
using F by (intro compact_chain [OF _ _ *]; blast dest: *)
qed
text‹The Baire property of dense sets›
theorem Baire:
fixes S::"'a::{real_normed_vector,heine_borel} set"
assumes "closed S" "countable 𝒢"
and ope: "⋀T. T ∈ 𝒢 ⟹ openin (top_of_set S) T ∧ S ⊆ closure T"
shows "S ⊆ closure(⋂𝒢)"
proof (cases "𝒢 = {}")
case True
then show ?thesis
using closure_subset by auto
next
let ?g = "from_nat_into 𝒢"
case False
then have gin: "?g n ∈ 𝒢" for n
by (simp add: from_nat_into)
show ?thesis
proof (clarsimp simp: closure_approachable)
fix x and e::real
assume "x ∈ S" "0 < e"
obtain TF where opeF: "⋀n. openin (top_of_set S) (TF n)"
and ne: "⋀n. TF n ≠ {}"
and subg: "⋀n. S ∩ closure(TF n) ⊆ ?g n"
and subball: "⋀n. closure(TF n) ⊆ ball x e"
and decr: "⋀n. TF(Suc n) ⊆ TF n"
proof -
have *: "∃Y. (openin (top_of_set S) Y ∧ Y ≠ {} ∧
S ∩ closure Y ⊆ ?g n ∧ closure Y ⊆ ball x e) ∧ Y ⊆ U"
if opeU: "openin (top_of_set S) U" and "U ≠ {}" and cloU: "closure U ⊆ ball x e" for U n
proof -
obtain T where T: "open T" "U = T ∩ S"
using ‹openin (top_of_set S) U› by (auto simp: openin_subtopology)
with ‹U ≠ {}› have "T ∩ closure (?g n) ≠ {}"
using gin ope by fastforce
then have "T ∩ ?g n ≠ {}"
using ‹open T› open_Int_closure_eq_empty by blast
then obtain y where "y ∈ U" "y ∈ ?g n"
using T ope [of "?g n", OF gin] by (blast dest: openin_imp_subset)
moreover have "openin (top_of_set S) (U ∩ ?g n)"
using gin ope opeU by blast
ultimately obtain d where U: "U ∩ ?g n ⊆ S" and "d > 0" and d: "ball y d ∩ S ⊆ U ∩ ?g n"
by (force simp: openin_contains_ball)
show ?thesis
proof (intro exI conjI)
show "openin (top_of_set S) (S ∩ ball y (d/2))"
by (simp add: openin_open_Int)
show "S ∩ ball y (d/2) ≠ {}"
using ‹0 < d› ‹y ∈ U› opeU openin_imp_subset by fastforce
have "S ∩ closure (S ∩ ball y (d/2)) ⊆ S ∩ closure (ball y (d/2))"
using closure_mono by blast
also have "... ⊆ ?g n"
using ‹d > 0› d by force
finally show "S ∩ closure (S ∩ ball y (d/2)) ⊆ ?g n" .
have "closure (S ∩ ball y (d/2)) ⊆ S ∩ ball y d"
proof -
have "closure (ball y (d/2)) ⊆ ball y d"
using ‹d > 0› by auto
then have "closure (S ∩ ball y (d/2)) ⊆ ball y d"
by (meson closure_mono inf.cobounded2 subset_trans)
then show ?thesis
by (simp add: ‹closed S› closure_minimal)
qed
also have "... ⊆ ball x e"
using cloU closure_subset d by blast
finally show "closure (S ∩ ball y (d/2)) ⊆ ball x e" .
show "S ∩ ball y (d/2) ⊆ U"
using ball_divide_subset_numeral d by blast
qed
qed
let ?Φ = "λn X. openin (top_of_set S) X ∧ X ≠ {} ∧
S ∩ closure X ⊆ ?g n ∧ closure X ⊆ ball x e"
have "closure (S ∩ ball x (e/2)) ⊆ closure(ball x (e/2))"
by (simp add: closure_mono)
also have "... ⊆ ball x e"
using ‹e > 0› by auto
finally have "closure (S ∩ ball x (e/2)) ⊆ ball x e" .
moreover have"openin (top_of_set S) (S ∩ ball x (e/2))" "S ∩ ball x (e/2) ≠ {}"
using ‹0 < e› ‹x ∈ S› by auto
ultimately obtain Y where Y: "?Φ 0 Y ∧ Y ⊆ S ∩ ball x (e/2)"
using * [of "S ∩ ball x (e/2)" 0] by metis
show thesis
proof (rule exE [OF dependent_nat_choice])
show "∃x. ?Φ 0 x"
using Y by auto
show "∃Y. ?Φ (Suc n) Y ∧ Y ⊆ X" if "?Φ n X" for X n
using that by (blast intro: *)
qed (use that in metis)
qed
have "(⋂n. S ∩ closure (TF n)) ≠ {}"
proof (rule compact_nest)
show "⋀n. compact (S ∩ closure (TF n))"
by (metis closed_closure subball bounded_subset_ballI compact_eq_bounded_closed closed_Int_compact [OF ‹closed S›])
show "⋀n. S ∩ closure (TF n) ≠ {}"
by (metis Int_absorb1 opeF ‹closed S› closure_eq_empty closure_minimal ne openin_imp_subset)
show "⋀m n. m ≤ n ⟹ S ∩ closure (TF n) ⊆ S ∩ closure (TF m)"
by (meson closure_mono decr dual_order.refl inf_mono lift_Suc_antimono_le)
qed
moreover have "(⋂n. S ∩ closure (TF n)) ⊆ {y ∈ ⋂𝒢. dist y x < e}"
proof (clarsimp, intro conjI)
fix y
assume "y ∈ S" and y: "∀n. y ∈ closure (TF n)"
then show "∀T∈𝒢. y ∈ T"
by (metis Int_iff from_nat_into_surj [OF ‹countable 𝒢›] subsetD subg)
show "dist y x < e"
by (metis y dist_commute mem_ball subball subsetCE)
qed
ultimately show "∃y ∈ ⋂𝒢. dist y x < e"
by auto
qed
qed
subsection ‹Continuity›
subsubsection ‹Structural rules for uniform continuity›
lemma (in bounded_linear) uniformly_continuous_on[continuous_intros]:
fixes g :: "_::metric_space ⇒ _"
assumes "uniformly_continuous_on s g"
shows "uniformly_continuous_on s (λx. f (g x))"
using assms unfolding uniformly_continuous_on_sequentially
unfolding dist_norm tendsto_norm_zero_iff diff[symmetric]
by (auto intro: tendsto_zero)
lemma uniformly_continuous_on_dist[continuous_intros]:
fixes f g :: "'a::metric_space ⇒ 'b::metric_space"
assumes "uniformly_continuous_on s f"
and "uniformly_continuous_on s g"
shows "uniformly_continuous_on s (λx. dist (f x) (g x))"
proof -
{
fix a b c d :: 'b
have "¦dist a b - dist c d¦ ≤ dist a c + dist b d"
using dist_triangle2 [of a b c] dist_triangle2 [of b c d]
using dist_triangle3 [of c d a] dist_triangle [of a d b]
by arith
} note le = this
{
fix x y
assume f: "(λn. dist (f (x n)) (f (y n))) ⇢ 0"
assume g: "(λn. dist (g (x n)) (g (y n))) ⇢ 0"
have "(λn. ¦dist (f (x n)) (g (x n)) - dist (f (y n)) (g (y n))¦) ⇢ 0"
by (rule Lim_transform_bound [OF _ tendsto_add_zero [OF f g]],
simp add: le)
}
then show ?thesis
using assms unfolding uniformly_continuous_on_sequentially
unfolding dist_real_def by simp
qed
lemma uniformly_continuous_on_cmul_right [continuous_intros]:
fixes f :: "'a::real_normed_vector ⇒ 'b::real_normed_algebra"
shows "uniformly_continuous_on s f ⟹ uniformly_continuous_on s (λx. f x * c)"
using bounded_linear.uniformly_continuous_on[OF bounded_linear_mult_left] .
lemma uniformly_continuous_on_cmul_left[continuous_intros]:
fixes f :: "'a::real_normed_vector ⇒ 'b::real_normed_algebra"
assumes "uniformly_continuous_on s f"
shows "uniformly_continuous_on s (λx. c * f x)"
by (metis assms bounded_linear.uniformly_continuous_on bounded_linear_mult_right)
lemma uniformly_continuous_on_norm[continuous_intros]:
fixes f :: "'a :: metric_space ⇒ 'b :: real_normed_vector"
assumes "uniformly_continuous_on s f"
shows "uniformly_continuous_on s (λx. norm (f x))"
unfolding norm_conv_dist using assms
by (intro uniformly_continuous_on_dist uniformly_continuous_on_const)
lemma uniformly_continuous_on_cmul[continuous_intros]:
fixes f :: "'a::metric_space ⇒ 'b::real_normed_vector"
assumes "uniformly_continuous_on s f"
shows "uniformly_continuous_on s (λx. c *⇩R f(x))"
using bounded_linear_scaleR_right assms
by (rule bounded_linear.uniformly_continuous_on)
lemma dist_minus:
fixes x y :: "'a::real_normed_vector"
shows "dist (- x) (- y) = dist x y"
unfolding dist_norm minus_diff_minus norm_minus_cancel ..
lemma uniformly_continuous_on_minus[continuous_intros]:
fixes f :: "'a::metric_space ⇒ 'b::real_normed_vector"
shows "uniformly_continuous_on s f ⟹ uniformly_continuous_on s (λx. - f x)"
unfolding uniformly_continuous_on_def dist_minus .
lemma uniformly_continuous_on_add[continuous_intros]:
fixes f g :: "'a::metric_space ⇒ 'b::real_normed_vector"
assumes "uniformly_continuous_on s f"
and "uniformly_continuous_on s g"
shows "uniformly_continuous_on s (λx. f x + g x)"
using assms
unfolding uniformly_continuous_on_sequentially
unfolding dist_norm tendsto_norm_zero_iff add_diff_add
by (auto intro: tendsto_add_zero)
lemma uniformly_continuous_on_diff[continuous_intros]:
fixes f :: "'a::metric_space ⇒ 'b::real_normed_vector"
assumes "uniformly_continuous_on s f"
and "uniformly_continuous_on s g"
shows "uniformly_continuous_on s (λx. f x - g x)"
using assms uniformly_continuous_on_add [of s f "- g"]
by (simp add: fun_Compl_def uniformly_continuous_on_minus)
lemma uniformly_continuous_on_sum [continuous_intros]:
fixes f :: "'a ⇒ 'b::metric_space ⇒ 'c::real_normed_vector"
shows "(⋀i. i ∈ I ⟹ uniformly_continuous_on S (f i)) ⟹ uniformly_continuous_on S (λx. ∑i∈I. f i x)"
by (induction I rule: infinite_finite_induct)
(auto simp: uniformly_continuous_on_add uniformly_continuous_on_const)
subsection ‹Arithmetic Preserves Topological Properties›
lemma open_scaling[intro]:
fixes S :: "'a::real_normed_vector set"
assumes "c ≠ 0"
and "open S"
shows "open((λx. c *⇩R x) ` S)"
proof -
{
fix x
assume "x ∈ S"
then obtain ε where "ε>0"
and ε: "∀x'. dist x' x < ε ⟶ x' ∈ S" using assms(2)[unfolded open_dist, THEN bspec[where x=x]]
by auto
have "ε * ¦c¦ > 0"
using assms(1)[unfolded zero_less_abs_iff[symmetric]] ‹ε>0› by auto
moreover
{
fix y
assume "dist y (c *⇩R x) < ε * ¦c¦"
then have "norm (c *⇩R ((1 / c) *⇩R y - x)) < ε * norm c"
by (simp add: ‹c ≠ 0› dist_norm scale_right_diff_distrib)
then have "norm ((1 / c) *⇩R y - x) < ε"
by (simp add: ‹c ≠ 0›)
then have "y ∈ (*⇩R) c ` S"
using rev_image_eqI[of "(1 / c) *⇩R y" S y "(*⇩R) c"]
by (simp add: ‹c ≠ 0› dist_norm ε)
}
ultimately have "∃e>0. ∀x'. dist x' (c *⇩R x) < e ⟶ x' ∈ (*⇩R) c ` S"
by (rule_tac x="ε * ¦c¦" in exI, auto)
}
then show ?thesis unfolding open_dist by auto
qed
lemma open_times_image:
fixes S::"'a::real_normed_field set"
assumes "c≠0" "open S"
shows "open (((*) c) ` S)"
proof -
let ?f = "λx. x/c" and ?g="((*) c)"
have "continuous_on UNIV ?f" using ‹c≠0› by (auto intro:continuous_intros)
then have "open (?f -` S)" using ‹open S› by (auto elim:open_vimage)
moreover have "?g ` S = ?f -` S" using ‹c≠0›
using image_iff by fastforce
ultimately show ?thesis by auto
qed
lemma minus_image_eq_vimage:
fixes A :: "'a::ab_group_add set"
shows "(λx. - x) ` A = (λx. - x) -` A"
by (auto intro!: image_eqI [where f="λx. - x"])
lemma open_negations:
fixes S :: "'a::real_normed_vector set"
shows "open S ⟹ open ((λx. - x) ` S)"
using open_scaling [of "- 1" S] by simp
lemma open_translation:
fixes S :: "'a::real_normed_vector set"
assumes "open S"
shows "open((λx. a + x) ` S)"
proof -
{
fix x
have "continuous (at x) (λx. x - a)"
by (intro continuous_diff continuous_ident continuous_const)
}
moreover have "{x. x - a ∈ S} = (+) a ` S"
by force
ultimately show ?thesis
by (metis assms continuous_open_vimage vimage_def)
qed
lemma open_translation_subtract:
fixes S :: "'a::real_normed_vector set"
assumes "open S"
shows "open ((λx. x - a) ` S)"
using assms open_translation [of S "- a"] by (simp cong: image_cong_simp)
lemma open_neg_translation:
fixes S :: "'a::real_normed_vector set"
assumes "open S"
shows "open((λx. a - x) ` S)"
using open_translation[OF open_negations[OF assms], of a]
by (auto simp: image_image)
lemma open_affinity:
fixes S :: "'a::real_normed_vector set"
assumes "open S" "c ≠ 0"
shows "open ((λx. a + c *⇩R x) ` S)"
proof -
have *: "(λx. a + c *⇩R x) = (λx. a + x) ∘ (λx. c *⇩R x)"
unfolding o_def ..
have "(+) a ` (*⇩R) c ` S = ((+) a ∘ (*⇩R) c) ` S"
by auto
then show ?thesis
using assms open_translation[of "(*⇩R) c ` S" a]
unfolding *
by auto
qed
lemma interior_translation:
"interior ((+) a ` S) = (+) a ` (interior S)" for S :: "'a::real_normed_vector set"
proof (rule set_eqI, rule)
fix x
assume "x ∈ interior ((+) a ` S)"
then obtain e where "e > 0" and e: "ball x e ⊆ (+) a ` S"
unfolding mem_interior by auto
then have "ball (x - a) e ⊆ S"
unfolding subset_eq Ball_def mem_ball dist_norm
by (auto simp: diff_diff_eq)
then show "x ∈ (+) a ` interior S"
unfolding image_iff
by (metis ‹0 < e› add.commute diff_add_cancel mem_interior)
next
fix x
assume "x ∈ (+) a ` interior S"
then obtain y e where "e > 0" and e: "ball y e ⊆ S" and y: "x = a + y"
unfolding image_iff Bex_def mem_interior by auto
{
fix z
have *: "a + y - z = y + a - z" by auto
assume "z ∈ ball x e"
then have "z - a ∈ S"
using e[unfolded subset_eq, THEN bspec[where x="z - a"]]
unfolding mem_ball dist_norm y group_add_class.diff_diff_eq2 *
by auto
then have "z ∈ (+) a ` S"
unfolding image_iff by (auto intro!: bexI[where x="z - a"])
}
then have "ball x e ⊆ (+) a ` S"
unfolding subset_eq by auto
then show "x ∈ interior ((+) a ` S)"
unfolding mem_interior using ‹e > 0› by auto
qed
lemma interior_translation_subtract:
"interior ((λx. x - a) ` S) = (λx. x - a) ` interior S" for S :: "'a::real_normed_vector set"
using interior_translation [of "- a"] by (simp cong: image_cong_simp)
lemma compact_scaling:
fixes s :: "'a::real_normed_vector set"
assumes "compact s"
shows "compact ((λx. c *⇩R x) ` s)"
proof -
let ?f = "λx. scaleR c x"
have *: "bounded_linear ?f" by (rule bounded_linear_scaleR_right)
show ?thesis
using compact_continuous_image[of s ?f] continuous_at_imp_continuous_on[of s ?f]
using linear_continuous_at[OF *] assms
by auto
qed
lemma compact_negations:
fixes s :: "'a::real_normed_vector set"
assumes "compact s"
shows "compact ((λx. - x) ` s)"
using compact_scaling [OF assms, of "- 1"] by auto
lemma compact_sums:
fixes s t :: "'a::real_normed_vector set"
assumes "compact s"
and "compact t"
shows "compact {x + y | x y. x ∈ s ∧ y ∈ t}"
proof -
have *: "{x + y | x y. x ∈ s ∧ y ∈ t} = (λz. fst z + snd z) ` (s × t)"
by (fastforce simp: image_iff)
have "continuous_on (s × t) (λz. fst z + snd z)"
unfolding continuous_on by (rule ballI) (intro tendsto_intros)
then show ?thesis
unfolding * using compact_continuous_image compact_Times [OF assms] by auto
qed
lemma compact_differences:
fixes s t :: "'a::real_normed_vector set"
assumes "compact s"
and "compact t"
shows "compact {x - y | x y. x ∈ s ∧ y ∈ t}"
proof-
have "{x - y | x y. x∈s ∧ y ∈ t} = {x + y | x y. x ∈ s ∧ y ∈ (uminus ` t)}"
using diff_conv_add_uminus by force
then show ?thesis
using compact_sums[OF assms(1) compact_negations[OF assms(2)]] by auto
qed
lemma compact_sums':
fixes S :: "'a::real_normed_vector set"
assumes "compact S" and "compact T"
shows "compact (⋃x∈ S. ⋃y ∈ T. {x + y})"
proof -
have "(⋃x∈S. ⋃y∈T. {x + y}) = {x + y |x y. x ∈ S ∧ y ∈ T}"
by blast
then show ?thesis
using compact_sums [OF assms] by simp
qed
lemma compact_differences':
fixes S :: "'a::real_normed_vector set"
assumes "compact S" and "compact T"
shows "compact (⋃x∈ S. ⋃y ∈ T. {x - y})"
proof -
have "(⋃x∈S. ⋃y∈T. {x - y}) = {x - y |x y. x ∈ S ∧ y ∈ T}"
by blast
then show ?thesis
using compact_differences [OF assms] by simp
qed
lemma compact_translation:
"compact ((+) a ` s)" if "compact s" for s :: "'a::real_normed_vector set"
proof -
have "{x + y |x y. x ∈ s ∧ y ∈ {a}} = (λx. a + x) ` s"
by auto
then show ?thesis
using compact_sums [OF that compact_sing [of a]] by auto
qed
lemma compact_translation_subtract:
"compact ((λx. x - a) ` s)" if "compact s" for s :: "'a::real_normed_vector set"
using that compact_translation [of s "- a"] by (simp cong: image_cong_simp)
lemma compact_affinity:
fixes s :: "'a::real_normed_vector set"
assumes "compact s"
shows "compact ((λx. a + c *⇩R x) ` s)"
proof -
have "(+) a ` (*⇩R) c ` s = (λx. a + c *⇩R x) ` s"
by auto
then show ?thesis
using compact_translation[OF compact_scaling[OF assms], of a c] by auto
qed
lemma closed_scaling:
fixes S :: "'a::real_normed_vector set"
assumes "closed S"
shows "closed ((λx. c *⇩R x) ` S)"
proof (cases "c = 0")
case True then show ?thesis
by (auto simp: image_constant_conv)
next
case False
from assms have "closed ((λx. inverse c *⇩R x) -` S)"
by (simp add: continuous_closed_vimage)
also have "(λx. inverse c *⇩R x) -` S = (λx. c *⇩R x) ` S"
using ‹c ≠ 0› by (auto elim: image_eqI [rotated])
finally show ?thesis .
qed
lemma closed_negations:
fixes S :: "'a::real_normed_vector set"
assumes "closed S"
shows "closed ((λx. -x) ` S)"
using closed_scaling[OF assms, of "- 1"] by simp
lemma compact_closed_sums:
fixes S :: "'a::real_normed_vector set"
assumes "compact S" and "closed T"
shows "closed (⋃x∈ S. ⋃y ∈ T. {x + y})"
proof -
let ?S = "{x + y |x y. x ∈ S ∧ y ∈ T}"
{
fix x l
assume as: "∀n. x n ∈ ?S" "(x ⤏ l) sequentially"
from as(1) obtain f where f: "∀n. x n = fst (f n) + snd (f n)" "∀n. fst (f n) ∈ S" "∀n. snd (f n) ∈ T"
using choice[of "λn y. x n = (fst y) + (snd y) ∧ fst y ∈ S ∧ snd y ∈ T"] by auto
obtain l' r where "l'∈S" and r: "strict_mono r" and lr: "(((λn. fst (f n)) ∘ r) ⤏ l') sequentially"
using assms(1)[unfolded compact_def, THEN spec[where x="λ n. fst (f n)"]] using f(2) by auto
have "((λn. snd (f (r n))) ⤏ l - l') sequentially"
using tendsto_diff[OF LIMSEQ_subseq_LIMSEQ[OF as(2) r] lr] and f(1)
unfolding o_def
by auto
then have "l - l' ∈ T"
using assms(2)[unfolded closed_sequential_limits,
THEN spec[where x="λ n. snd (f (r n))"],
THEN spec[where x="l - l'"]]
using f(3)
by auto
then have "l ∈ ?S"
using ‹l' ∈ S› by force
}
moreover have "?S = (⋃x∈ S. ⋃y ∈ T. {x + y})"
by force
ultimately show ?thesis
unfolding closed_sequential_limits
by (metis (no_types, lifting))
qed
lemma closed_compact_sums:
fixes S T :: "'a::real_normed_vector set"
assumes "closed S" "compact T"
shows "closed (⋃x∈ S. ⋃y ∈ T. {x + y})"
proof -
have "(⋃x∈ T. ⋃y ∈ S. {x + y}) = (⋃x∈ S. ⋃y ∈ T. {x + y})"
by auto
then show ?thesis
using compact_closed_sums[OF assms(2,1)] by simp
qed
lemma compact_closed_differences:
fixes S T :: "'a::real_normed_vector set"
assumes "compact S" "closed T"
shows "closed (⋃x∈ S. ⋃y ∈ T. {x - y})"
proof -
have "(⋃x∈ S. ⋃y ∈ uminus ` T. {x + y}) = (⋃x∈ S. ⋃y ∈ T. {x - y})"
by force
then show ?thesis
by (metis assms closed_negations compact_closed_sums)
qed
lemma closed_compact_differences:
fixes S T :: "'a::real_normed_vector set"
assumes "closed S" "compact T"
shows "closed (⋃x∈ S. ⋃y ∈ T. {x - y})"
proof -
have "(⋃x∈ S. ⋃y ∈ uminus ` T. {x + y}) = {x - y |x y. x ∈ S ∧ y ∈ T}"
by auto
then show ?thesis
using closed_compact_sums[OF assms(1) compact_negations[OF assms(2)]] by simp
qed
lemma closed_translation:
"closed ((+) a ` S)" if "closed S" for a :: "'a::real_normed_vector"
proof -
have "(⋃x∈ {a}. ⋃y ∈ S. {x + y}) = ((+) a ` S)" by auto
then show ?thesis
using compact_closed_sums [OF compact_sing [of a] that] by auto
qed
lemma closed_translation_subtract:
"closed ((λx. x - a) ` S)" if "closed S" for a :: "'a::real_normed_vector"
using that closed_translation [of S "- a"] by (simp cong: image_cong_simp)
lemma closure_translation:
"closure ((+) a ` s) = (+) a ` closure s" for a :: "'a::real_normed_vector"
proof -
have *: "(+) a ` (- s) = - (+) a ` s"
by (auto intro!: image_eqI [where x = "x - a" for x])
show ?thesis
using interior_translation [of a "- s", symmetric]
by (simp add: closure_interior translation_Compl *)
qed
lemma closure_translation_subtract:
"closure ((λx. x - a) ` s) = (λx. x - a) ` closure s" for a :: "'a::real_normed_vector"
using closure_translation [of "- a" s] by (simp cong: image_cong_simp)
lemma frontier_translation:
"frontier ((+) a ` s) = (+) a ` frontier s" for a :: "'a::real_normed_vector"
by (auto simp add: frontier_def translation_diff interior_translation closure_translation)
lemma frontier_translation_subtract:
"frontier ((+) a ` s) = (+) a ` frontier s" for a :: "'a::real_normed_vector"
by (auto simp add: frontier_def translation_diff interior_translation closure_translation)
lemma sphere_translation:
"sphere (a + c) r = (+) a ` sphere c r" for a :: "'n::real_normed_vector"
by (auto simp: dist_norm algebra_simps intro!: image_eqI [where x = "x - a" for x])
lemma sphere_translation_subtract:
"sphere (c - a) r = (λx. x - a) ` sphere c r" for a :: "'n::real_normed_vector"
using sphere_translation [of "- a" c] by (simp cong: image_cong_simp)
lemma cball_translation:
"cball (a + c) r = (+) a ` cball c r" for a :: "'n::real_normed_vector"
by (auto simp: dist_norm algebra_simps intro!: image_eqI [where x = "x - a" for x])
lemma cball_translation_subtract:
"cball (c - a) r = (λx. x - a) ` cball c r" for a :: "'n::real_normed_vector"
using cball_translation [of "- a" c] by (simp cong: image_cong_simp)
lemma ball_translation:
"ball (a + c) r = (+) a ` ball c r" for a :: "'n::real_normed_vector"
by (auto simp: dist_norm algebra_simps intro!: image_eqI [where x = "x - a" for x])
lemma ball_translation_subtract:
"ball (c - a) r = (λx. x - a) ` ball c r" for a :: "'n::real_normed_vector"
using ball_translation [of "- a" c] by (simp cong: image_cong_simp)
subsection‹Homeomorphisms›
lemma homeomorphic_scaling:
fixes S :: "'a::real_normed_vector set"
assumes "c ≠ 0"
shows "S homeomorphic ((λx. c *⇩R x) ` S)"
unfolding homeomorphic_minimal
apply (rule_tac x="λx. c *⇩R x" in exI)
apply (rule_tac x="λx. (1 / c) *⇩R x" in exI)
using assms by (auto simp: continuous_intros)
lemma homeomorphic_translation:
fixes S :: "'a::real_normed_vector set"
shows "S homeomorphic ((λx. a + x) ` S)"
unfolding homeomorphic_minimal
apply (rule_tac x="λx. a + x" in exI)
apply (rule_tac x="λx. -a + x" in exI)
by (auto simp: continuous_intros)
lemma homeomorphic_affinity:
fixes S :: "'a::real_normed_vector set"
assumes "c ≠ 0"
shows "S homeomorphic ((λx. a + c *⇩R x) ` S)"
proof -
have *: "(+) a ` (*⇩R) c ` S = (λx. a + c *⇩R x) ` S" by auto
show ?thesis
by (metis "*" assms homeomorphic_scaling homeomorphic_trans homeomorphic_translation)
qed
lemma homeomorphic_balls:
fixes a b ::"'a::real_normed_vector"
assumes "0 < d" "0 < e"
shows "(ball a d) homeomorphic (ball b e)" (is ?th)
and "(cball a d) homeomorphic (cball b e)" (is ?cth)
proof -
show ?th unfolding homeomorphic_minimal
apply(rule_tac x="λx. b + (e/d) *⇩R (x - a)" in exI)
apply(rule_tac x="λx. a + (d/e) *⇩R (x - b)" in exI)
using assms
by (auto intro!: continuous_intros simp: dist_commute dist_norm pos_divide_less_eq)
show ?cth unfolding homeomorphic_minimal
apply(rule_tac x="λx. b + (e/d) *⇩R (x - a)" in exI)
apply(rule_tac x="λx. a + (d/e) *⇩R (x - b)" in exI)
using assms
by (auto intro!: continuous_intros simp: dist_commute dist_norm pos_divide_le_eq)
qed
lemma homeomorphic_spheres:
fixes a b ::"'a::real_normed_vector"
assumes "0 < d" "0 < e"
shows "(sphere a d) homeomorphic (sphere b e)"
unfolding homeomorphic_minimal
apply(rule_tac x="λx. b + (e/d) *⇩R (x - a)" in exI)
apply(rule_tac x="λx. a + (d/e) *⇩R (x - b)" in exI)
using assms
by (auto intro!: continuous_intros simp: dist_commute dist_norm pos_divide_less_eq)
lemma homeomorphic_ball01_UNIV:
"ball (0::'a::real_normed_vector) 1 homeomorphic (UNIV:: 'a set)"
(is "?B homeomorphic ?U")
proof
have "x ∈ (λz. z /⇩R (1 - norm z)) ` ball 0 1" for x::'a
apply (rule_tac x="x /⇩R (1 + norm x)" in image_eqI)
apply (auto simp: field_split_simps)
using norm_ge_zero [of x] apply linarith+
done
then show "(λz::'a. z /⇩R (1 - norm z)) ` ?B = ?U"
by blast
have "x ∈ range (λz. (1 / (1 + norm z)) *⇩R z)" if "norm x < 1" for x::'a
using that
by (rule_tac x="x /⇩R (1 - norm x)" in image_eqI) (auto simp: field_split_simps)
then show "(λz::'a. z /⇩R (1 + norm z)) ` ?U = ?B"
by (force simp: field_split_simps dest: add_less_zeroD)
show "continuous_on (ball 0 1) (λz. z /⇩R (1 - norm z))"
by (rule continuous_intros | force)+
have 0: "⋀z. 1 + norm z ≠ 0"
by (metis (no_types) le_add_same_cancel1 norm_ge_zero not_one_le_zero)
then show "continuous_on UNIV (λz. z /⇩R (1 + norm z))"
by (auto intro!: continuous_intros)
show "⋀x. x ∈ ball 0 1 ⟹
x /⇩R (1 - norm x) /⇩R (1 + norm (x /⇩R (1 - norm x))) = x"
by (auto simp: field_split_simps)
show "⋀y. y /⇩R (1 + norm y) /⇩R (1 - norm (y /⇩R (1 + norm y))) = y"
using 0 by (auto simp: field_split_simps)
qed
proposition homeomorphic_ball_UNIV:
fixes a ::"'a::real_normed_vector"
assumes "0 < r" shows "ball a r homeomorphic (UNIV:: 'a set)"
using assms homeomorphic_ball01_UNIV homeomorphic_balls(1) homeomorphic_trans zero_less_one by blast
subsection ‹Discrete›
lemma finite_implies_discrete:
fixes S :: "'a::topological_space set"
assumes "finite (f ` S)"
shows "(∀x ∈ S. ∃e>0. ∀y. y ∈ S ∧ f y ≠ f x ⟶ e ≤ norm (f y - f x))"
proof -
have "∃e>0. ∀y. y ∈ S ∧ f y ≠ f x ⟶ e ≤ norm (f y - f x)" if "x ∈ S" for x
proof (cases "f ` S - {f x} = {}")
case True
with zero_less_numeral show ?thesis
by (fastforce simp add: Set.image_subset_iff cong: conj_cong)
next
case False
then obtain z where "z ∈ S" "f z ≠ f x"
by blast
moreover have finn: "finite {norm (z - f x) |z. z ∈ f ` S - {f x}}"
using assms by simp
ultimately have *: "0 < Inf{norm(z - f x) | z. z ∈ f ` S - {f x}}"
by (force intro: finite_imp_less_Inf)
show ?thesis
by (force intro!: * cInf_le_finite [OF finn])
qed
with assms show ?thesis
by blast
qed
subsection ‹Completeness of "Isometry" (up to constant bounds)›
lemma cauchy_isometric:
assumes e: "e > 0"
and s: "subspace s"
and f: "bounded_linear f"
and normf: "∀x∈s. norm (f x) ≥ e * norm x"
and xs: "∀n. x n ∈ s"
and cf: "Cauchy (f ∘ x)"
shows "Cauchy x"
proof -
interpret f: bounded_linear f by fact
have "∃N. ∀n≥N. norm (x n - x N) < d" if "d > 0" for d :: real
proof -
from that obtain N where N: "∀n≥N. norm (f (x n) - f (x N)) < e * d"
using cf[unfolded Cauchy_def o_def dist_norm, THEN spec[where x="e*d"]] e
by auto
have "norm (x n - x N) < d" if "n ≥ N" for n
proof -
have "e * norm (x n - x N) ≤ norm (f (x n - x N))"
using subspace_diff[OF s, of "x n" "x N"]
using xs[THEN spec[where x=N]] and xs[THEN spec[where x=n]]
using normf[THEN bspec[where x="x n - x N"]]
by auto
also have "norm (f (x n - x N)) < e * d"
using ‹N ≤ n› N unfolding f.diff[symmetric] by auto
finally show ?thesis
using ‹e>0› by simp
qed
then show ?thesis by auto
qed
then show ?thesis
by (simp add: Cauchy_altdef2 dist_norm)
qed
lemma complete_isometric_image:
assumes "0 < e"
and s: "subspace s"
and f: "bounded_linear f"
and normf: "∀x∈s. norm(f x) ≥ e * norm(x)"
and cs: "complete s"
shows "complete (f ` s)"
proof -
have "∃l∈f ` s. (g ⤏ l) sequentially"
if as:"∀n::nat. g n ∈ f ` s" and cfg:"Cauchy g" for g
proof -
from that obtain x where "∀n. x n ∈ s ∧ g n = f (x n)"
using choice[of "λ n xa. xa ∈ s ∧ g n = f xa"] by auto
then have x: "∀n. x n ∈ s" "∀n. g n = f (x n)" by auto
then have "f ∘ x = g" by (simp add: fun_eq_iff)
then obtain l where "l∈s" and l:"(x ⤏ l) sequentially"
using cs[unfolded complete_def, THEN spec[where x=x]]
using cauchy_isometric[OF ‹0 < e› s f normf] and cfg and x(1)
by auto
then show ?thesis
using linear_continuous_at[OF f, unfolded continuous_at_sequentially, THEN spec[where x=x], of l]
by (auto simp: ‹f ∘ x = g›)
qed
then show ?thesis
unfolding complete_def by auto
qed
subsection ‹Connected Normed Spaces›
lemma compact_components:
fixes s :: "'a::heine_borel set"
shows "⟦compact s; c ∈ components s⟧ ⟹ compact c"
by (meson bounded_subset closed_components in_components_subset compact_eq_bounded_closed)
lemma discrete_subset_disconnected:
fixes S :: "'a::topological_space set"
fixes t :: "'b::real_normed_vector set"
assumes conf: "continuous_on S f"
and no: "⋀x. x ∈ S ⟹ ∃e>0. ∀y. y ∈ S ∧ f y ≠ f x ⟶ e ≤ norm (f y - f x)"
shows "f ` S ⊆ {y. connected_component_set (f ` S) y = {y}}"
proof -
{ fix x assume x: "x ∈ S"
then obtain e where "e>0" and ele: "⋀y. ⟦y ∈ S; f y ≠ f x⟧ ⟹ e ≤ norm (f y - f x)"
using conf no [OF x] by auto
then have e2: "0 ≤ e/2"
by simp
define F where "F ≡ connected_component_set (f ` S) (f x)"
have False if "y ∈ S" and ccs: "f y ∈ F" and not: "f y ≠ f x" for y
proof -
define C where "C ≡ cball (f x) (e/2)"
define D where "D ≡ - ball (f x) e"
have disj: "C ∩ D = {}"
unfolding C_def D_def using ‹0 < e› by fastforce
moreover have FCD: "F ⊆ C ∪ D"
proof -
have "t ∈ C ∨ t ∈ D" if "t ∈ F" for t
proof -
obtain y where "y ∈ S" "t = f y"
using F_def ‹t ∈ F› connected_component_in by blast
then show ?thesis
by (metis C_def ComplI D_def centre_in_cball dist_norm e2 ele mem_ball norm_minus_commute not_le)
qed
then show ?thesis
by auto
qed
ultimately have "C ∩ F = {} ∨ D ∩ F = {}"
using connected_closed [of "F"] ‹e>0› not
unfolding C_def D_def
by (metis Elementary_Metric_Spaces.open_ball F_def closed_cball connected_connected_component inf_bot_left open_closed)
moreover have "C ∩ F ≠ {}"
unfolding disjoint_iff
by (metis FCD ComplD image_eqI mem_Collect_eq subsetD x D_def F_def Un_iff ‹0 < e› centre_in_ball connected_component_refl_eq)
moreover have "D ∩ F ≠ {}"
unfolding disjoint_iff
by (metis ComplI D_def ccs dist_norm ele mem_ball norm_minus_commute not not_le that(1))
ultimately show ?thesis by metis
qed
moreover have "connected_component_set (f ` S) (f x) ⊆ f ` S"
by (auto simp: connected_component_in)
ultimately have "connected_component_set (f ` S) (f x) = {f x}"
by (auto simp: x F_def)
}
with assms show ?thesis
by blast
qed
lemma continuous_disconnected_range_constant_eq:
"(connected S ⟷
(∀f::'a::topological_space ⇒ 'b::real_normed_algebra_1.
∀t. continuous_on S f ∧ f ` S ⊆ t ∧ (∀y ∈ t. connected_component_set t y = {y})
⟶ f constant_on S))" (is ?thesis1)
and continuous_discrete_range_constant_eq:
"(connected S ⟷
(∀f::'a::topological_space ⇒ 'b::real_normed_algebra_1.
continuous_on S f ∧
(∀x ∈ S. ∃e. 0 < e ∧ (∀y. y ∈ S ∧ (f y ≠ f x) ⟶ e ≤ norm(f y - f x)))
⟶ f constant_on S))" (is ?thesis2)
and continuous_finite_range_constant_eq:
"(connected S ⟷
(∀f::'a::topological_space ⇒ 'b::real_normed_algebra_1.
continuous_on S f ∧ finite (f ` S)
⟶ f constant_on S))" (is ?thesis3)
proof -
have *: "⋀s t u v. ⟦s ⟹ t; t ⟹ u; u ⟹ v; v ⟹ s⟧
⟹ (s ⟷ t) ∧ (s ⟷ u) ∧ (s ⟷ v)"
by blast
have "?thesis1 ∧ ?thesis2 ∧ ?thesis3"
apply (rule *)
using continuous_disconnected_range_constant
apply (metis image_subset_iff_funcset)
apply (smt (verit, best) discrete_subset_disconnected mem_Collect_eq subsetD subsetI)
apply (blast dest: finite_implies_discrete)
apply (blast intro!: finite_range_constant_imp_connected)
done
then show ?thesis1 ?thesis2 ?thesis3
by blast+
qed
lemma continuous_discrete_range_constant:
fixes f :: "'a::topological_space ⇒ 'b::real_normed_algebra_1"
assumes S: "connected S"
and "continuous_on S f"
and "⋀x. x ∈ S ⟹ ∃e>0. ∀y. y ∈ S ∧ f y ≠ f x ⟶ e ≤ norm (f y - f x)"
shows "f constant_on S"
using continuous_discrete_range_constant_eq [THEN iffD1, OF S] assms by blast
lemma continuous_finite_range_constant:
fixes f :: "'a::topological_space ⇒ 'b::real_normed_algebra_1"
assumes "connected S"
and "continuous_on S f"
and "finite (f ` S)"
shows "f constant_on S"
using assms continuous_finite_range_constant_eq by blast
end