--- a/src/HOL/Analysis/Riemann_Mapping.thy Tue Dec 03 15:20:30 2019 +0100
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,1489 +0,0 @@
-(* Title: HOL/Analysis/Riemann_Mapping.thy
- Authors: LC Paulson, based on material from HOL Light
-*)
-
-section \<open>Moebius functions, Equivalents of Simply Connected Sets, Riemann Mapping Theorem\<close>
-
-theory Riemann_Mapping
-imports Great_Picard
-begin
-
-subsection\<open>Moebius functions are biholomorphisms of the unit disc\<close>
-
-definition\<^marker>\<open>tag important\<close> Moebius_function :: "[real,complex,complex] \<Rightarrow> complex" where
- "Moebius_function \<equiv> \<lambda>t w z. exp(\<i> * of_real t) * (z - w) / (1 - cnj w * z)"
-
-lemma Moebius_function_simple:
- "Moebius_function 0 w z = (z - w) / (1 - cnj w * z)"
- by (simp add: Moebius_function_def)
-
-lemma Moebius_function_eq_zero:
- "Moebius_function t w w = 0"
- by (simp add: Moebius_function_def)
-
-lemma Moebius_function_of_zero:
- "Moebius_function t w 0 = - exp(\<i> * of_real t) * w"
- by (simp add: Moebius_function_def)
-
-lemma Moebius_function_norm_lt_1:
- assumes w1: "norm w < 1" and z1: "norm z < 1"
- shows "norm (Moebius_function t w z) < 1"
-proof -
- have "1 - cnj w * z \<noteq> 0"
- by (metis complex_cnj_cnj complex_mod_sqrt_Re_mult_cnj mult.commute mult_less_cancel_right1 norm_ge_zero norm_mult norm_one order.asym right_minus_eq w1 z1)
- then have VV: "1 - w * cnj z \<noteq> 0"
- by (metis complex_cnj_cnj complex_cnj_mult complex_cnj_one right_minus_eq)
- then have "1 - norm (Moebius_function t w z) ^ 2 =
- ((1 - norm w ^ 2) / (norm (1 - cnj w * z) ^ 2)) * (1 - norm z ^ 2)"
- apply (cases w)
- apply (cases z)
- apply (simp add: Moebius_function_def divide_simps norm_divide norm_mult)
- apply (simp add: complex_norm complex_diff complex_mult one_complex.code complex_cnj)
- apply (auto simp: algebra_simps power2_eq_square)
- done
- then have "1 - (cmod (Moebius_function t w z))\<^sup>2 = (1 - cmod (w * w)) / (cmod (1 - cnj w * z))\<^sup>2 * (1 - cmod (z * z))"
- by (simp add: norm_mult power2_eq_square)
- moreover have "0 < 1 - cmod (z * z)"
- by (metis (no_types) z1 diff_gt_0_iff_gt mult.left_neutral norm_mult_less)
- ultimately have "0 < 1 - norm (Moebius_function t w z) ^ 2"
- using \<open>1 - cnj w * z \<noteq> 0\<close> w1 norm_mult_less by fastforce
- then show ?thesis
- using linorder_not_less by fastforce
-qed
-
-lemma Moebius_function_holomorphic:
- assumes "norm w < 1"
- shows "Moebius_function t w holomorphic_on ball 0 1"
-proof -
- have *: "1 - z * w \<noteq> 0" if "norm z < 1" for z
- proof -
- have "norm (1::complex) \<noteq> norm (z * w)"
- using assms that norm_mult_less by fastforce
- then show ?thesis by auto
- qed
- show ?thesis
- apply (simp add: Moebius_function_def)
- apply (intro holomorphic_intros)
- using assms *
- by (metis complex_cnj_cnj complex_cnj_mult complex_cnj_one complex_mod_cnj mem_ball_0 mult.commute right_minus_eq)
-qed
-
-lemma Moebius_function_compose:
- assumes meq: "-w1 = w2" and "norm w1 < 1" "norm z < 1"
- shows "Moebius_function 0 w1 (Moebius_function 0 w2 z) = z"
-proof -
- have "norm w2 < 1"
- using assms by auto
- then have "-w1 = z" if "cnj w2 * z = 1"
- by (metis assms(3) complex_mod_cnj less_irrefl mult.right_neutral norm_mult_less norm_one that)
- moreover have "z=0" if "1 - cnj w2 * z = cnj w1 * (z - w2)"
- proof -
- have "w2 * cnj w2 = 1"
- using that meq by (auto simp: algebra_simps)
- then show "z = 0"
- by (metis (no_types) \<open>cmod w2 < 1\<close> complex_mod_cnj less_irrefl mult.right_neutral norm_mult_less norm_one)
- qed
- moreover have "z - w2 - w1 * (1 - cnj w2 * z) = z * (1 - cnj w2 * z - cnj w1 * (z - w2))"
- using meq by (fastforce simp: algebra_simps)
- ultimately
- show ?thesis
- by (simp add: Moebius_function_def divide_simps norm_divide norm_mult)
-qed
-
-lemma ball_biholomorphism_exists:
- assumes "a \<in> ball 0 1"
- obtains f g where "f a = 0"
- "f holomorphic_on ball 0 1" "f ` ball 0 1 \<subseteq> ball 0 1"
- "g holomorphic_on ball 0 1" "g ` ball 0 1 \<subseteq> ball 0 1"
- "\<And>z. z \<in> ball 0 1 \<Longrightarrow> f (g z) = z"
- "\<And>z. z \<in> ball 0 1 \<Longrightarrow> g (f z) = z"
-proof
- show "Moebius_function 0 a holomorphic_on ball 0 1" "Moebius_function 0 (-a) holomorphic_on ball 0 1"
- using Moebius_function_holomorphic assms by auto
- show "Moebius_function 0 a a = 0"
- by (simp add: Moebius_function_eq_zero)
- show "Moebius_function 0 a ` ball 0 1 \<subseteq> ball 0 1"
- "Moebius_function 0 (- a) ` ball 0 1 \<subseteq> ball 0 1"
- using Moebius_function_norm_lt_1 assms by auto
- show "Moebius_function 0 a (Moebius_function 0 (- a) z) = z"
- "Moebius_function 0 (- a) (Moebius_function 0 a z) = z" if "z \<in> ball 0 1" for z
- using Moebius_function_compose assms that by auto
-qed
-
-
-subsection\<open>A big chain of equivalents of simple connectedness for an open set\<close>
-
-lemma biholomorphic_to_disc_aux:
- assumes "open S" "connected S" "0 \<in> S" and S01: "S \<subseteq> ball 0 1"
- and prev: "\<And>f. \<lbrakk>f holomorphic_on S; \<And>z. z \<in> S \<Longrightarrow> f z \<noteq> 0; inj_on f S\<rbrakk>
- \<Longrightarrow> \<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)"
- shows "\<exists>f g. f holomorphic_on S \<and> g holomorphic_on ball 0 1 \<and>
- (\<forall>z \<in> S. f z \<in> ball 0 1 \<and> g(f z) = z) \<and>
- (\<forall>z \<in> ball 0 1. g z \<in> S \<and> f(g z) = z)"
-proof -
- define F where "F \<equiv> {h. h holomorphic_on S \<and> h ` S \<subseteq> ball 0 1 \<and> h 0 = 0 \<and> inj_on h S}"
- have idF: "id \<in> F"
- using S01 by (auto simp: F_def)
- then have "F \<noteq> {}"
- by blast
- have imF_ne: "((\<lambda>h. norm(deriv h 0)) ` F) \<noteq> {}"
- using idF by auto
- have holF: "\<And>h. h \<in> F \<Longrightarrow> h holomorphic_on S"
- by (auto simp: F_def)
- obtain f where "f \<in> F" and normf: "\<And>h. h \<in> F \<Longrightarrow> norm(deriv h 0) \<le> norm(deriv f 0)"
- proof -
- obtain r where "r > 0" and r: "ball 0 r \<subseteq> S"
- using \<open>open S\<close> \<open>0 \<in> S\<close> openE by auto
- have bdd: "bdd_above ((\<lambda>h. norm(deriv h 0)) ` F)"
- proof (intro bdd_aboveI exI ballI, clarify)
- show "norm (deriv f 0) \<le> 1 / r" if "f \<in> F" for f
- proof -
- have r01: "(*) (complex_of_real r) ` ball 0 1 \<subseteq> S"
- using that \<open>r > 0\<close> by (auto simp: norm_mult r [THEN subsetD])
- then have "f holomorphic_on (*) (complex_of_real r) ` ball 0 1"
- using holomorphic_on_subset [OF holF] by (simp add: that)
- then have holf: "f \<circ> (\<lambda>z. (r * z)) holomorphic_on (ball 0 1)"
- by (intro holomorphic_intros holomorphic_on_compose)
- have f0: "(f \<circ> (*) (complex_of_real r)) 0 = 0"
- using F_def that by auto
- have "f ` S \<subseteq> ball 0 1"
- using F_def that by blast
- with r01 have fr1: "\<And>z. norm z < 1 \<Longrightarrow> norm ((f \<circ> (*)(of_real r))z) < 1"
- by force
- have *: "((\<lambda>w. f (r * w)) has_field_derivative deriv f (r * z) * r) (at z)"
- if "z \<in> ball 0 1" for z::complex
- proof (rule DERIV_chain' [where g=f])
- show "(f has_field_derivative deriv f (of_real r * z)) (at (of_real r * z))"
- apply (rule holomorphic_derivI [OF holF \<open>open S\<close>])
- apply (rule \<open>f \<in> F\<close>)
- by (meson imageI r01 subset_iff that)
- qed simp
- have df0: "((\<lambda>w. f (r * w)) has_field_derivative deriv f 0 * r) (at 0)"
- using * [of 0] by simp
- have deq: "deriv (\<lambda>x. f (complex_of_real r * x)) 0 = deriv f 0 * complex_of_real r"
- using DERIV_imp_deriv df0 by blast
- have "norm (deriv (f \<circ> (*) (complex_of_real r)) 0) \<le> 1"
- by (auto intro: Schwarz_Lemma [OF holf f0 fr1, of 0])
- with \<open>r > 0\<close> show ?thesis
- by (simp add: deq norm_mult divide_simps o_def)
- qed
- qed
- define l where "l \<equiv> SUP h\<in>F. norm (deriv h 0)"
- have eql: "norm (deriv f 0) = l" if le: "l \<le> norm (deriv f 0)" and "f \<in> F" for f
- apply (rule order_antisym [OF _ le])
- using \<open>f \<in> F\<close> bdd cSUP_upper by (fastforce simp: l_def)
- obtain \<F> where \<F>in: "\<And>n. \<F> n \<in> F" and \<F>lim: "(\<lambda>n. norm (deriv (\<F> n) 0)) \<longlonglongrightarrow> l"
- proof -
- have "\<exists>f. f \<in> F \<and> \<bar>norm (deriv f 0) - l\<bar> < 1 / (Suc n)" for n
- proof -
- obtain f where "f \<in> F" and f: "l < norm (deriv f 0) + 1/(Suc n)"
- using cSup_least [OF imF_ne, of "l - 1/(Suc n)"] by (fastforce simp add: l_def)
- then have "\<bar>norm (deriv f 0) - l\<bar> < 1 / (Suc n)"
- by (fastforce simp add: abs_if not_less eql)
- with \<open>f \<in> F\<close> show ?thesis
- by blast
- qed
- then obtain \<F> where fF: "\<And>n. (\<F> n) \<in> F"
- and fless: "\<And>n. \<bar>norm (deriv (\<F> n) 0) - l\<bar> < 1 / (Suc n)"
- by metis
- have "(\<lambda>n. norm (deriv (\<F> n) 0)) \<longlonglongrightarrow> l"
- proof (rule metric_LIMSEQ_I)
- fix e::real
- assume "e > 0"
- then obtain N::nat where N: "e > 1/(Suc N)"
- using nat_approx_posE by blast
- show "\<exists>N. \<forall>n\<ge>N. dist (norm (deriv (\<F> n) 0)) l < e"
- proof (intro exI allI impI)
- fix n assume "N \<le> n"
- have "dist (norm (deriv (\<F> n) 0)) l < 1 / (Suc n)"
- using fless by (simp add: dist_norm)
- also have "... < e"
- using N \<open>N \<le> n\<close> inverse_of_nat_le le_less_trans by blast
- finally show "dist (norm (deriv (\<F> n) 0)) l < e" .
- qed
- qed
- with fF show ?thesis
- using that by blast
- qed
- have "\<And>K. \<lbrakk>compact K; K \<subseteq> S\<rbrakk> \<Longrightarrow> \<exists>B. \<forall>h\<in>F. \<forall>z\<in>K. norm (h z) \<le> B"
- by (rule_tac x=1 in exI) (force simp: F_def)
- moreover have "range \<F> \<subseteq> F"
- using \<open>\<And>n. \<F> n \<in> F\<close> by blast
- ultimately obtain f and r :: "nat \<Rightarrow> nat"
- where holf: "f holomorphic_on S" and r: "strict_mono r"
- and limf: "\<And>x. x \<in> S \<Longrightarrow> (\<lambda>n. \<F> (r n) x) \<longlonglongrightarrow> f x"
- and ulimf: "\<And>K. \<lbrakk>compact K; K \<subseteq> S\<rbrakk> \<Longrightarrow> uniform_limit K (\<F> \<circ> r) f sequentially"
- using Montel [of S F \<F>, OF \<open>open S\<close> holF] by auto+
- have der: "\<And>n x. x \<in> S \<Longrightarrow> ((\<F> \<circ> r) n has_field_derivative ((\<lambda>n. deriv (\<F> n)) \<circ> r) n x) (at x)"
- using \<open>\<And>n. \<F> n \<in> F\<close> \<open>open S\<close> holF holomorphic_derivI by fastforce
- have ulim: "\<And>x. x \<in> S \<Longrightarrow> \<exists>d>0. cball x d \<subseteq> S \<and> uniform_limit (cball x d) (\<F> \<circ> r) f sequentially"
- by (meson ulimf \<open>open S\<close> compact_cball open_contains_cball)
- obtain f' :: "complex\<Rightarrow>complex" where f': "(f has_field_derivative f' 0) (at 0)"
- and tof'0: "(\<lambda>n. ((\<lambda>n. deriv (\<F> n)) \<circ> r) n 0) \<longlonglongrightarrow> f' 0"
- using has_complex_derivative_uniform_sequence [OF \<open>open S\<close> der ulim] \<open>0 \<in> S\<close> by metis
- then have derf0: "deriv f 0 = f' 0"
- by (simp add: DERIV_imp_deriv)
- have "f field_differentiable (at 0)"
- using field_differentiable_def f' by blast
- have "(\<lambda>x. (norm (deriv (\<F> (r x)) 0))) \<longlonglongrightarrow> norm (deriv f 0)"
- using isCont_tendsto_compose [OF continuous_norm [OF continuous_ident] tof'0] derf0 by auto
- with LIMSEQ_subseq_LIMSEQ [OF \<F>lim r] have no_df0: "norm(deriv f 0) = l"
- by (force simp: o_def intro: tendsto_unique)
- have nonconstf: "\<not> f constant_on S"
- proof -
- have False if "\<And>x. x \<in> S \<Longrightarrow> f x = c" for c
- proof -
- have "deriv f 0 = 0"
- by (metis that \<open>open S\<close> \<open>0 \<in> S\<close> DERIV_imp_deriv [OF has_field_derivative_transform_within_open [OF DERIV_const]])
- with no_df0 have "l = 0"
- by auto
- with eql [OF _ idF] show False by auto
- qed
- then show ?thesis
- by (meson constant_on_def)
- qed
- show ?thesis
- proof
- show "f \<in> F"
- unfolding F_def
- proof (intro CollectI conjI holf)
- have "norm(f z) \<le> 1" if "z \<in> S" for z
- proof (intro Lim_norm_ubound [OF _ limf] always_eventually allI that)
- fix n
- have "\<F> (r n) \<in> F"
- by (simp add: \<F>in)
- then show "norm (\<F> (r n) z) \<le> 1"
- using that by (auto simp: F_def)
- qed simp
- then have fless1: "norm(f z) < 1" if "z \<in> S" for z
- using maximum_modulus_principle [OF holf \<open>open S\<close> \<open>connected S\<close> \<open>open S\<close>] nonconstf that
- by fastforce
- then show "f ` S \<subseteq> ball 0 1"
- by auto
- have "(\<lambda>n. \<F> (r n) 0) \<longlonglongrightarrow> 0"
- using \<F>in by (auto simp: F_def)
- then show "f 0 = 0"
- using tendsto_unique [OF _ limf ] \<open>0 \<in> S\<close> trivial_limit_sequentially by blast
- show "inj_on f S"
- proof (rule Hurwitz_injective [OF \<open>open S\<close> \<open>connected S\<close> _ holf])
- show "\<And>n. (\<F> \<circ> r) n holomorphic_on S"
- by (simp add: \<F>in holF)
- show "\<And>K. \<lbrakk>compact K; K \<subseteq> S\<rbrakk> \<Longrightarrow> uniform_limit K(\<F> \<circ> r) f sequentially"
- by (metis ulimf)
- show "\<not> f constant_on S"
- using nonconstf by auto
- show "\<And>n. inj_on ((\<F> \<circ> r) n) S"
- using \<F>in by (auto simp: F_def)
- qed
- qed
- show "\<And>h. h \<in> F \<Longrightarrow> norm (deriv h 0) \<le> norm (deriv f 0)"
- by (metis eql le_cases no_df0)
- qed
- qed
- have holf: "f holomorphic_on S" and injf: "inj_on f S" and f01: "f ` S \<subseteq> ball 0 1"
- using \<open>f \<in> F\<close> by (auto simp: F_def)
- obtain g where holg: "g holomorphic_on (f ` S)"
- and derg: "\<And>z. z \<in> S \<Longrightarrow> deriv f z * deriv g (f z) = 1"
- and gf: "\<And>z. z \<in> S \<Longrightarrow> g(f z) = z"
- using holomorphic_has_inverse [OF holf \<open>open S\<close> injf] by metis
- have "ball 0 1 \<subseteq> f ` S"
- proof
- fix a::complex
- assume a: "a \<in> ball 0 1"
- have False if "\<And>x. x \<in> S \<Longrightarrow> f x \<noteq> a"
- proof -
- obtain h k where "h a = 0"
- and holh: "h holomorphic_on ball 0 1" and h01: "h ` ball 0 1 \<subseteq> ball 0 1"
- and holk: "k holomorphic_on ball 0 1" and k01: "k ` ball 0 1 \<subseteq> ball 0 1"
- and hk: "\<And>z. z \<in> ball 0 1 \<Longrightarrow> h (k z) = z"
- and kh: "\<And>z. z \<in> ball 0 1 \<Longrightarrow> k (h z) = z"
- using ball_biholomorphism_exists [OF a] by blast
- have nf1: "\<And>z. z \<in> S \<Longrightarrow> norm(f z) < 1"
- using \<open>f \<in> F\<close> by (auto simp: F_def)
- have 1: "h \<circ> f holomorphic_on S"
- using F_def \<open>f \<in> F\<close> holh holomorphic_on_compose holomorphic_on_subset by blast
- have 2: "\<And>z. z \<in> S \<Longrightarrow> (h \<circ> f) z \<noteq> 0"
- by (metis \<open>h a = 0\<close> a comp_eq_dest_lhs nf1 kh mem_ball_0 that)
- have 3: "inj_on (h \<circ> f) S"
- by (metis (no_types, lifting) F_def \<open>f \<in> F\<close> comp_inj_on inj_on_inverseI injf kh mem_Collect_eq subset_inj_on)
- obtain \<psi> where hol\<psi>: "\<psi> holomorphic_on ((h \<circ> f) ` S)"
- and \<psi>2: "\<And>z. z \<in> S \<Longrightarrow> \<psi>(h (f z)) ^ 2 = h(f z)"
- proof (rule exE [OF prev [OF 1 2 3]], safe)
- fix \<theta>
- assume hol\<theta>: "\<theta> holomorphic_on S" and \<theta>2: "(\<forall>z\<in>S. (h \<circ> f) z = (\<theta> z)\<^sup>2)"
- show thesis
- proof
- show "(\<theta> \<circ> g \<circ> k) holomorphic_on (h \<circ> f) ` S"
- proof (intro holomorphic_on_compose)
- show "k holomorphic_on (h \<circ> f) ` S"
- apply (rule holomorphic_on_subset [OF holk])
- using f01 h01 by force
- show "g holomorphic_on k ` (h \<circ> f) ` S"
- apply (rule holomorphic_on_subset [OF holg])
- by (auto simp: kh nf1)
- show "\<theta> holomorphic_on g ` k ` (h \<circ> f) ` S"
- apply (rule holomorphic_on_subset [OF hol\<theta>])
- by (auto simp: gf kh nf1)
- qed
- show "((\<theta> \<circ> g \<circ> k) (h (f z)))\<^sup>2 = h (f z)" if "z \<in> S" for z
- proof -
- have "f z \<in> ball 0 1"
- by (simp add: nf1 that)
- then have "(\<theta> (g (k (h (f z)))))\<^sup>2 = (\<theta> (g (f z)))\<^sup>2"
- by (metis kh)
- also have "... = h (f z)"
- using \<theta>2 gf that by auto
- finally show ?thesis
- by (simp add: o_def)
- qed
- qed
- qed
- have norm\<psi>1: "norm(\<psi> (h (f z))) < 1" if "z \<in> S" for z
- proof -
- have "norm (\<psi> (h (f z)) ^ 2) < 1"
- by (metis (no_types) that DIM_complex \<psi>2 h01 image_subset_iff mem_ball_0 nf1)
- then show ?thesis
- by (metis le_less_trans mult_less_cancel_left2 norm_ge_zero norm_power not_le power2_eq_square)
- qed
- then have \<psi>01: "\<psi> (h (f 0)) \<in> ball 0 1"
- by (simp add: \<open>0 \<in> S\<close>)
- obtain p q where p0: "p (\<psi> (h (f 0))) = 0"
- and holp: "p holomorphic_on ball 0 1" and p01: "p ` ball 0 1 \<subseteq> ball 0 1"
- and holq: "q holomorphic_on ball 0 1" and q01: "q ` ball 0 1 \<subseteq> ball 0 1"
- and pq: "\<And>z. z \<in> ball 0 1 \<Longrightarrow> p (q z) = z"
- and qp: "\<And>z. z \<in> ball 0 1 \<Longrightarrow> q (p z) = z"
- using ball_biholomorphism_exists [OF \<psi>01] by metis
- have "p \<circ> \<psi> \<circ> h \<circ> f \<in> F"
- unfolding F_def
- proof (intro CollectI conjI holf)
- show "p \<circ> \<psi> \<circ> h \<circ> f holomorphic_on S"
- proof (intro holomorphic_on_compose holf)
- show "h holomorphic_on f ` S"
- apply (rule holomorphic_on_subset [OF holh])
- using f01 by force
- show "\<psi> holomorphic_on h ` f ` S"
- apply (rule holomorphic_on_subset [OF hol\<psi>])
- by auto
- show "p holomorphic_on \<psi> ` h ` f ` S"
- apply (rule holomorphic_on_subset [OF holp])
- by (auto simp: norm\<psi>1)
- qed
- show "(p \<circ> \<psi> \<circ> h \<circ> f) ` S \<subseteq> ball 0 1"
- apply clarsimp
- by (meson norm\<psi>1 p01 image_subset_iff mem_ball_0)
- show "(p \<circ> \<psi> \<circ> h \<circ> f) 0 = 0"
- by (simp add: \<open>p (\<psi> (h (f 0))) = 0\<close>)
- show "inj_on (p \<circ> \<psi> \<circ> h \<circ> f) S"
- unfolding inj_on_def o_def
- by (metis \<psi>2 dist_0_norm gf kh mem_ball nf1 norm\<psi>1 qp)
- qed
- then have le_norm_df0: "norm (deriv (p \<circ> \<psi> \<circ> h \<circ> f) 0) \<le> norm (deriv f 0)"
- by (rule normf)
- have 1: "k \<circ> power2 \<circ> q holomorphic_on ball 0 1"
- proof (intro holomorphic_on_compose holq)
- show "power2 holomorphic_on q ` ball 0 1"
- using holomorphic_on_subset holomorphic_on_power
- by (blast intro: holomorphic_on_ident)
- show "k holomorphic_on power2 ` q ` ball 0 1"
- apply (rule holomorphic_on_subset [OF holk])
- using q01 by (auto simp: norm_power abs_square_less_1)
- qed
- have 2: "(k \<circ> power2 \<circ> q) 0 = 0"
- using p0 F_def \<open>f \<in> F\<close> \<psi>01 \<psi>2 \<open>0 \<in> S\<close> kh qp by force
- have 3: "norm ((k \<circ> power2 \<circ> q) z) < 1" if "norm z < 1" for z
- proof -
- have "norm ((power2 \<circ> q) z) < 1"
- using that q01 by (force simp: norm_power abs_square_less_1)
- with k01 show ?thesis
- by fastforce
- qed
- have False if c: "\<forall>z. norm z < 1 \<longrightarrow> (k \<circ> power2 \<circ> q) z = c * z" and "norm c = 1" for c
- proof -
- have "c \<noteq> 0" using that by auto
- have "norm (p(1/2)) < 1" "norm (p(-1/2)) < 1"
- using p01 by force+
- then have "(k \<circ> power2 \<circ> q) (p(1/2)) = c * p(1/2)" "(k \<circ> power2 \<circ> q) (p(-1/2)) = c * p(-1/2)"
- using c by force+
- then have "p (1/2) = p (- (1/2))"
- by (auto simp: \<open>c \<noteq> 0\<close> qp o_def)
- then have "q (p (1/2)) = q (p (- (1/2)))"
- by simp
- then have "1/2 = - (1/2::complex)"
- by (auto simp: qp)
- then show False
- by simp
- qed
- moreover
- have False if "norm (deriv (k \<circ> power2 \<circ> q) 0) \<noteq> 1" "norm (deriv (k \<circ> power2 \<circ> q) 0) \<le> 1"
- and le: "\<And>\<xi>. norm \<xi> < 1 \<Longrightarrow> norm ((k \<circ> power2 \<circ> q) \<xi>) \<le> norm \<xi>"
- proof -
- have "norm (deriv (k \<circ> power2 \<circ> q) 0) < 1"
- using that by simp
- moreover have eq: "deriv f 0 = deriv (k \<circ> (\<lambda>z. z ^ 2) \<circ> q) 0 * deriv (p \<circ> \<psi> \<circ> h \<circ> f) 0"
- proof (intro DERIV_imp_deriv has_field_derivative_transform_within_open [OF DERIV_chain])
- show "(k \<circ> power2 \<circ> q has_field_derivative deriv (k \<circ> power2 \<circ> q) 0) (at ((p \<circ> \<psi> \<circ> h \<circ> f) 0))"
- using "1" holomorphic_derivI p0 by auto
- show "(p \<circ> \<psi> \<circ> h \<circ> f has_field_derivative deriv (p \<circ> \<psi> \<circ> h \<circ> f) 0) (at 0)"
- using \<open>p \<circ> \<psi> \<circ> h \<circ> f \<in> F\<close> \<open>open S\<close> \<open>0 \<in> S\<close> holF holomorphic_derivI by blast
- show "\<And>x. x \<in> S \<Longrightarrow> (k \<circ> power2 \<circ> q \<circ> (p \<circ> \<psi> \<circ> h \<circ> f)) x = f x"
- using \<psi>2 f01 kh norm\<psi>1 qp by auto
- qed (use assms in simp_all)
- ultimately have "cmod (deriv (p \<circ> \<psi> \<circ> h \<circ> f) 0) \<le> 0"
- using le_norm_df0
- by (metis linorder_not_le mult.commute mult_less_cancel_left2 norm_mult)
- moreover have "1 \<le> norm (deriv f 0)"
- using normf [of id] by (simp add: idF)
- ultimately show False
- by (simp add: eq)
- qed
- ultimately show ?thesis
- using Schwarz_Lemma [OF 1 2 3] norm_one by blast
- qed
- then show "a \<in> f ` S"
- by blast
- qed
- then have "f ` S = ball 0 1"
- using F_def \<open>f \<in> F\<close> by blast
- then show ?thesis
- apply (rule_tac x=f in exI)
- apply (rule_tac x=g in exI)
- using holf holg derg gf by safe force+
-qed
-
-
-locale SC_Chain =
- fixes S :: "complex set"
- assumes openS: "open S"
-begin
-
-lemma winding_number_zero:
- assumes "simply_connected S"
- shows "connected S \<and>
- (\<forall>\<gamma> z. path \<gamma> \<and> path_image \<gamma> \<subseteq> S \<and>
- pathfinish \<gamma> = pathstart \<gamma> \<and> z \<notin> S \<longrightarrow> winding_number \<gamma> z = 0)"
- using assms
- by (auto simp: simply_connected_imp_connected simply_connected_imp_winding_number_zero)
-
-lemma contour_integral_zero:
- assumes "valid_path g" "path_image g \<subseteq> S" "pathfinish g = pathstart g" "f holomorphic_on S"
- "\<And>\<gamma> z. \<lbrakk>path \<gamma>; path_image \<gamma> \<subseteq> S; pathfinish \<gamma> = pathstart \<gamma>; z \<notin> S\<rbrakk> \<Longrightarrow> winding_number \<gamma> z = 0"
- shows "(f has_contour_integral 0) g"
- using assms by (meson Cauchy_theorem_global openS valid_path_imp_path)
-
-lemma global_primitive:
- assumes "connected S" and holf: "f holomorphic_on S"
- and prev: "\<And>\<gamma> f. \<lbrakk>valid_path \<gamma>; path_image \<gamma> \<subseteq> S; pathfinish \<gamma> = pathstart \<gamma>; f holomorphic_on S\<rbrakk> \<Longrightarrow> (f has_contour_integral 0) \<gamma>"
- shows "\<exists>h. \<forall>z \<in> S. (h has_field_derivative f z) (at z)"
-proof (cases "S = {}")
-case True then show ?thesis
- by simp
-next
- case False
- then obtain a where "a \<in> S"
- by blast
- show ?thesis
- proof (intro exI ballI)
- fix x assume "x \<in> S"
- then obtain d where "d > 0" and d: "cball x d \<subseteq> S"
- using openS open_contains_cball_eq by blast
- let ?g = "\<lambda>z. (SOME g. polynomial_function g \<and> path_image g \<subseteq> S \<and> pathstart g = a \<and> pathfinish g = z)"
- show "((\<lambda>z. contour_integral (?g z) f) has_field_derivative f x)
- (at x)"
- proof (simp add: has_field_derivative_def has_derivative_at2 bounded_linear_mult_right, rule Lim_transform)
- show "(\<lambda>y. inverse(norm(y - x)) *\<^sub>R (contour_integral(linepath x y) f - f x * (y - x))) \<midarrow>x\<rightarrow> 0"
- proof (clarsimp simp add: Lim_at)
- fix e::real assume "e > 0"
- moreover have "continuous (at x) f"
- using openS \<open>x \<in> S\<close> holf continuous_on_eq_continuous_at holomorphic_on_imp_continuous_on by auto
- ultimately obtain d1 where "d1 > 0"
- and d1: "\<And>x'. dist x' x < d1 \<Longrightarrow> dist (f x') (f x) < e/2"
- unfolding continuous_at_eps_delta
- by (metis less_divide_eq_numeral1(1) mult_zero_left)
- obtain d2 where "d2 > 0" and d2: "ball x d2 \<subseteq> S"
- using openS \<open>x \<in> S\<close> open_contains_ball_eq by blast
- have "inverse (norm (y - x)) * norm (contour_integral (linepath x y) f - f x * (y - x)) < e"
- if "0 < d1" "0 < d2" "y \<noteq> x" "dist y x < d1" "dist y x < d2" for y
- proof -
- have "f contour_integrable_on linepath x y"
- proof (rule contour_integrable_continuous_linepath [OF continuous_on_subset])
- show "continuous_on S f"
- by (simp add: holf holomorphic_on_imp_continuous_on)
- have "closed_segment x y \<subseteq> ball x d2"
- by (meson dist_commute_lessI dist_in_closed_segment le_less_trans mem_ball subsetI that(5))
- with d2 show "closed_segment x y \<subseteq> S"
- by blast
- qed
- then obtain z where z: "(f has_contour_integral z) (linepath x y)"
- by (force simp: contour_integrable_on_def)
- have con: "((\<lambda>w. f x) has_contour_integral f x * (y - x)) (linepath x y)"
- using has_contour_integral_const_linepath [of "f x" y x] by metis
- have "norm (z - f x * (y - x)) \<le> (e/2) * norm (y - x)"
- proof (rule has_contour_integral_bound_linepath)
- show "((\<lambda>w. f w - f x) has_contour_integral z - f x * (y - x)) (linepath x y)"
- by (rule has_contour_integral_diff [OF z con])
- show "\<And>w. w \<in> closed_segment x y \<Longrightarrow> norm (f w - f x) \<le> e/2"
- by (metis d1 dist_norm less_le_trans not_less not_less_iff_gr_or_eq segment_bound1 that(4))
- qed (use \<open>e > 0\<close> in auto)
- with \<open>e > 0\<close> have "inverse (norm (y - x)) * norm (z - f x * (y - x)) \<le> e/2"
- by (simp add: field_split_simps)
- also have "... < e"
- using \<open>e > 0\<close> by simp
- finally show ?thesis
- by (simp add: contour_integral_unique [OF z])
- qed
- with \<open>d1 > 0\<close> \<open>d2 > 0\<close>
- show "\<exists>d>0. \<forall>z. z \<noteq> x \<and> dist z x < d \<longrightarrow>
- inverse (norm (z - x)) * norm (contour_integral (linepath x z) f - f x * (z - x)) < e"
- by (rule_tac x="min d1 d2" in exI) auto
- qed
- next
- have *: "(1 / norm (y - x)) *\<^sub>R (contour_integral (?g y) f -
- (contour_integral (?g x) f + f x * (y - x))) =
- (contour_integral (linepath x y) f - f x * (y - x)) /\<^sub>R norm (y - x)"
- if "0 < d" "y \<noteq> x" and yx: "dist y x < d" for y
- proof -
- have "y \<in> S"
- by (metis subsetD d dist_commute less_eq_real_def mem_cball yx)
- have gxy: "polynomial_function (?g x) \<and> path_image (?g x) \<subseteq> S \<and> pathstart (?g x) = a \<and> pathfinish (?g x) = x"
- "polynomial_function (?g y) \<and> path_image (?g y) \<subseteq> S \<and> pathstart (?g y) = a \<and> pathfinish (?g y) = y"
- using someI_ex [OF connected_open_polynomial_connected [OF openS \<open>connected S\<close> \<open>a \<in> S\<close>]] \<open>x \<in> S\<close> \<open>y \<in> S\<close>
- by meson+
- then have vp: "valid_path (?g x)" "valid_path (?g y)"
- by (simp_all add: valid_path_polynomial_function)
- have f0: "(f has_contour_integral 0) ((?g x) +++ linepath x y +++ reversepath (?g y))"
- proof (rule prev)
- show "valid_path ((?g x) +++ linepath x y +++ reversepath (?g y))"
- using gxy vp by (auto simp: valid_path_join)
- have "closed_segment x y \<subseteq> cball x d"
- using yx by (auto simp: dist_commute dest!: dist_in_closed_segment)
- then have "closed_segment x y \<subseteq> S"
- using d by blast
- then show "path_image ((?g x) +++ linepath x y +++ reversepath (?g y)) \<subseteq> S"
- using gxy by (auto simp: path_image_join)
- qed (use gxy holf in auto)
- then have fintxy: "f contour_integrable_on linepath x y"
- by (metis (no_types, lifting) contour_integrable_joinD1 contour_integrable_joinD2 gxy(2) has_contour_integral_integrable pathfinish_linepath pathstart_reversepath valid_path_imp_reverse valid_path_join valid_path_linepath vp(2))
- have fintgx: "f contour_integrable_on (?g x)" "f contour_integrable_on (?g y)"
- using openS contour_integrable_holomorphic_simple gxy holf vp by blast+
- show ?thesis
- apply (clarsimp simp add: divide_simps)
- using contour_integral_unique [OF f0]
- apply (simp add: fintxy gxy contour_integrable_reversepath contour_integral_reversepath fintgx vp)
- apply (simp add: algebra_simps)
- done
- qed
- show "(\<lambda>z. (1 / norm (z - x)) *\<^sub>R
- (contour_integral (?g z) f - (contour_integral (?g x) f + f x * (z - x))) -
- (contour_integral (linepath x z) f - f x * (z - x)) /\<^sub>R norm (z - x))
- \<midarrow>x\<rightarrow> 0"
- apply (rule tendsto_eventually)
- apply (simp add: eventually_at)
- apply (rule_tac x=d in exI)
- using \<open>d > 0\<close> * by simp
- qed
- qed
-qed
-
-lemma holomorphic_log:
- assumes "connected S" and holf: "f holomorphic_on S" and nz: "\<And>z. z \<in> S \<Longrightarrow> f z \<noteq> 0"
- and prev: "\<And>f. f holomorphic_on S \<Longrightarrow> \<exists>h. \<forall>z \<in> S. (h has_field_derivative f z) (at z)"
- shows "\<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = exp(g z))"
-proof -
- have "(\<lambda>z. deriv f z / f z) holomorphic_on S"
- by (simp add: openS holf holomorphic_deriv holomorphic_on_divide nz)
- then obtain g where g: "\<And>z. z \<in> S \<Longrightarrow> (g has_field_derivative deriv f z / f z) (at z)"
- using prev [of "\<lambda>z. deriv f z / f z"] by metis
- have hfd: "\<And>x. x \<in> S \<Longrightarrow> ((\<lambda>z. exp (g z) / f z) has_field_derivative 0) (at x)"
- apply (rule derivative_eq_intros g| simp)+
- apply (subst DERIV_deriv_iff_field_differentiable)
- using openS holf holomorphic_on_imp_differentiable_at nz apply auto
- done
- obtain c where c: "\<And>x. x \<in> S \<Longrightarrow> exp (g x) / f x = c"
- proof (rule DERIV_zero_connected_constant[OF \<open>connected S\<close> openS finite.emptyI])
- show "continuous_on S (\<lambda>z. exp (g z) / f z)"
- by (metis (full_types) openS g continuous_on_divide continuous_on_exp holf holomorphic_on_imp_continuous_on holomorphic_on_open nz)
- then show "\<forall>x\<in>S - {}. ((\<lambda>z. exp (g z) / f z) has_field_derivative 0) (at x)"
- using hfd by (blast intro: DERIV_zero_connected_constant [OF \<open>connected S\<close> openS finite.emptyI, of "\<lambda>z. exp(g z) / f z"])
- qed auto
- show ?thesis
- proof (intro exI ballI conjI)
- show "(\<lambda>z. Ln(inverse c) + g z) holomorphic_on S"
- apply (intro holomorphic_intros)
- using openS g holomorphic_on_open by blast
- fix z :: complex
- assume "z \<in> S"
- then have "exp (g z) / c = f z"
- by (metis c divide_divide_eq_right exp_not_eq_zero nonzero_mult_div_cancel_left)
- moreover have "1 / c \<noteq> 0"
- using \<open>z \<in> S\<close> c nz by fastforce
- ultimately show "f z = exp (Ln (inverse c) + g z)"
- by (simp add: exp_add inverse_eq_divide)
- qed
-qed
-
-lemma holomorphic_sqrt:
- assumes holf: "f holomorphic_on S" and nz: "\<And>z. z \<in> S \<Longrightarrow> f z \<noteq> 0"
- and prev: "\<And>f. \<lbrakk>f holomorphic_on S; \<forall>z \<in> S. f z \<noteq> 0\<rbrakk> \<Longrightarrow> \<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = exp(g z))"
- shows "\<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)"
-proof -
- obtain g where holg: "g holomorphic_on S" and g: "\<And>z. z \<in> S \<Longrightarrow> f z = exp (g z)"
- using prev [of f] holf nz by metis
- show ?thesis
- proof (intro exI ballI conjI)
- show "(\<lambda>z. exp(g z/2)) holomorphic_on S"
- by (intro holomorphic_intros) (auto simp: holg)
- show "\<And>z. z \<in> S \<Longrightarrow> f z = (exp (g z/2))\<^sup>2"
- by (metis (no_types) g exp_double nonzero_mult_div_cancel_left times_divide_eq_right zero_neq_numeral)
- qed
-qed
-
-lemma biholomorphic_to_disc:
- assumes "connected S" and S: "S \<noteq> {}" "S \<noteq> UNIV"
- and prev: "\<And>f. \<lbrakk>f holomorphic_on S; \<forall>z \<in> S. f z \<noteq> 0\<rbrakk> \<Longrightarrow> \<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)"
- shows "\<exists>f g. f holomorphic_on S \<and> g holomorphic_on ball 0 1 \<and>
- (\<forall>z \<in> S. f z \<in> ball 0 1 \<and> g(f z) = z) \<and>
- (\<forall>z \<in> ball 0 1. g z \<in> S \<and> f(g z) = z)"
-proof -
- obtain a b where "a \<in> S" "b \<notin> S"
- using S by blast
- then obtain \<delta> where "\<delta> > 0" and \<delta>: "ball a \<delta> \<subseteq> S"
- using openS openE by blast
- obtain g where holg: "g holomorphic_on S" and eqg: "\<And>z. z \<in> S \<Longrightarrow> z - b = (g z)\<^sup>2"
- proof (rule exE [OF prev [of "\<lambda>z. z - b"]])
- show "(\<lambda>z. z - b) holomorphic_on S"
- by (intro holomorphic_intros)
- qed (use \<open>b \<notin> S\<close> in auto)
- have "\<not> g constant_on S"
- proof -
- have "(a + \<delta>/2) \<in> ball a \<delta>" "a + (\<delta>/2) \<noteq> a"
- using \<open>\<delta> > 0\<close> by (simp_all add: dist_norm)
- then show ?thesis
- unfolding constant_on_def
- using eqg [of a] eqg [of "a + \<delta>/2"] \<open>a \<in> S\<close> \<delta>
- by (metis diff_add_cancel subset_eq)
- qed
- then have "open (g ` ball a \<delta>)"
- using open_mapping_thm [of g S "ball a \<delta>", OF holg openS \<open>connected S\<close>] \<delta> by blast
- then obtain r where "r > 0" and r: "ball (g a) r \<subseteq> (g ` ball a \<delta>)"
- by (metis \<open>0 < \<delta>\<close> centre_in_ball imageI openE)
- have g_not_r: "g z \<notin> ball (-(g a)) r" if "z \<in> S" for z
- proof
- assume "g z \<in> ball (-(g a)) r"
- then have "- g z \<in> ball (g a) r"
- by (metis add.inverse_inverse dist_minus mem_ball)
- with r have "- g z \<in> (g ` ball a \<delta>)"
- by blast
- then obtain w where w: "- g z = g w" "dist a w < \<delta>"
- by auto
- then have "w \<in> ball a \<delta>"
- by simp
- then have "w \<in> S"
- using \<delta> by blast
- then have "w = z"
- by (metis diff_add_cancel eqg power_minus_Bit0 that w(1))
- then have "g z = 0"
- using \<open>- g z = g w\<close> by auto
- with eqg [OF that] have "z = b"
- by auto
- with that \<open>b \<notin> S\<close> show False
- by simp
- qed
- then have nz: "\<And>z. z \<in> S \<Longrightarrow> g z + g a \<noteq> 0"
- by (metis \<open>0 < r\<close> add.commute add_diff_cancel_left' centre_in_ball diff_0)
- let ?f = "\<lambda>z. (r/3) / (g z + g a) - (r/3) / (g a + g a)"
- obtain h where holh: "h holomorphic_on S" and "h a = 0" and h01: "h ` S \<subseteq> ball 0 1" and "inj_on h S"
- proof
- show "?f holomorphic_on S"
- by (intro holomorphic_intros holg nz)
- have 3: "\<lbrakk>norm x \<le> 1/3; norm y \<le> 1/3\<rbrakk> \<Longrightarrow> norm(x - y) < 1" for x y::complex
- using norm_triangle_ineq4 [of x y] by simp
- have "norm ((r/3) / (g z + g a) - (r/3) / (g a + g a)) < 1" if "z \<in> S" for z
- apply (rule 3)
- unfolding norm_divide
- using \<open>r > 0\<close> g_not_r [OF \<open>z \<in> S\<close>] g_not_r [OF \<open>a \<in> S\<close>]
- by (simp_all add: field_split_simps dist_commute dist_norm)
- then show "?f ` S \<subseteq> ball 0 1"
- by auto
- show "inj_on ?f S"
- using \<open>r > 0\<close> eqg apply (clarsimp simp: inj_on_def)
- by (metis diff_add_cancel)
- qed auto
- obtain k where holk: "k holomorphic_on (h ` S)"
- and derk: "\<And>z. z \<in> S \<Longrightarrow> deriv h z * deriv k (h z) = 1"
- and kh: "\<And>z. z \<in> S \<Longrightarrow> k(h z) = z"
- using holomorphic_has_inverse [OF holh openS \<open>inj_on h S\<close>] by metis
-
- have 1: "open (h ` S)"
- by (simp add: \<open>inj_on h S\<close> holh openS open_mapping_thm3)
- have 2: "connected (h ` S)"
- by (simp add: connected_continuous_image \<open>connected S\<close> holh holomorphic_on_imp_continuous_on)
- have 3: "0 \<in> h ` S"
- using \<open>a \<in> S\<close> \<open>h a = 0\<close> by auto
- have 4: "\<exists>g. g holomorphic_on h ` S \<and> (\<forall>z\<in>h ` S. f z = (g z)\<^sup>2)"
- if holf: "f holomorphic_on h ` S" and nz: "\<And>z. z \<in> h ` S \<Longrightarrow> f z \<noteq> 0" "inj_on f (h ` S)" for f
- proof -
- obtain g where holg: "g holomorphic_on S" and eqg: "\<And>z. z \<in> S \<Longrightarrow> (f \<circ> h) z = (g z)\<^sup>2"
- proof -
- have "f \<circ> h holomorphic_on S"
- by (simp add: holh holomorphic_on_compose holf)
- moreover have "\<forall>z\<in>S. (f \<circ> h) z \<noteq> 0"
- by (simp add: nz)
- ultimately show thesis
- using prev that by blast
- qed
- show ?thesis
- proof (intro exI conjI)
- show "g \<circ> k holomorphic_on h ` S"
- proof -
- have "k ` h ` S \<subseteq> S"
- by (simp add: \<open>\<And>z. z \<in> S \<Longrightarrow> k (h z) = z\<close> image_subset_iff)
- then show ?thesis
- by (meson holg holk holomorphic_on_compose holomorphic_on_subset)
- qed
- show "\<forall>z\<in>h ` S. f z = ((g \<circ> k) z)\<^sup>2"
- using eqg kh by auto
- qed
- qed
- obtain f g where f: "f holomorphic_on h ` S" and g: "g holomorphic_on ball 0 1"
- and gf: "\<forall>z\<in>h ` S. f z \<in> ball 0 1 \<and> g (f z) = z" and fg:"\<forall>z\<in>ball 0 1. g z \<in> h ` S \<and> f (g z) = z"
- using biholomorphic_to_disc_aux [OF 1 2 3 h01 4] by blast
- show ?thesis
- proof (intro exI conjI)
- show "f \<circ> h holomorphic_on S"
- by (simp add: f holh holomorphic_on_compose)
- show "k \<circ> g holomorphic_on ball 0 1"
- by (metis holomorphic_on_subset image_subset_iff fg holk g holomorphic_on_compose)
- qed (use fg gf kh in auto)
-qed
-
-lemma homeomorphic_to_disc:
- assumes S: "S \<noteq> {}"
- and prev: "S = UNIV \<or>
- (\<exists>f g. f holomorphic_on S \<and> g holomorphic_on ball 0 1 \<and>
- (\<forall>z \<in> S. f z \<in> ball 0 1 \<and> g(f z) = z) \<and>
- (\<forall>z \<in> ball 0 1. g z \<in> S \<and> f(g z) = z))" (is "_ \<or> ?P")
- shows "S homeomorphic ball (0::complex) 1"
- using prev
-proof
- assume "S = UNIV" then show ?thesis
- using homeomorphic_ball01_UNIV homeomorphic_sym by blast
-next
- assume ?P
- then show ?thesis
- unfolding homeomorphic_minimal
- using holomorphic_on_imp_continuous_on by blast
-qed
-
-lemma homeomorphic_to_disc_imp_simply_connected:
- assumes "S = {} \<or> S homeomorphic ball (0::complex) 1"
- shows "simply_connected S"
- using assms homeomorphic_simply_connected_eq convex_imp_simply_connected by auto
-
-end
-
-proposition
- assumes "open S"
- shows simply_connected_eq_winding_number_zero:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>g z. path g \<and> path_image g \<subseteq> S \<and>
- pathfinish g = pathstart g \<and> (z \<notin> S)
- \<longrightarrow> winding_number g z = 0)" (is "?wn0")
- and simply_connected_eq_contour_integral_zero:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>g f. valid_path g \<and> path_image g \<subseteq> S \<and>
- pathfinish g = pathstart g \<and> f holomorphic_on S
- \<longrightarrow> (f has_contour_integral 0) g)" (is "?ci0")
- and simply_connected_eq_global_primitive:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>f. f holomorphic_on S \<longrightarrow>
- (\<exists>h. \<forall>z. z \<in> S \<longrightarrow> (h has_field_derivative f z) (at z)))" (is "?gp")
- and simply_connected_eq_holomorphic_log:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>f. f holomorphic_on S \<and> (\<forall>z \<in> S. f z \<noteq> 0)
- \<longrightarrow> (\<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = exp(g z))))" (is "?log")
- and simply_connected_eq_holomorphic_sqrt:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>f. f holomorphic_on S \<and> (\<forall>z \<in> S. f z \<noteq> 0)
- \<longrightarrow> (\<exists>g. g holomorphic_on S \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)))" (is "?sqrt")
- and simply_connected_eq_biholomorphic_to_disc:
- "simply_connected S \<longleftrightarrow>
- S = {} \<or> S = UNIV \<or>
- (\<exists>f g. f holomorphic_on S \<and> g holomorphic_on ball 0 1 \<and>
- (\<forall>z \<in> S. f z \<in> ball 0 1 \<and> g(f z) = z) \<and>
- (\<forall>z \<in> ball 0 1. g z \<in> S \<and> f(g z) = z))" (is "?bih")
- and simply_connected_eq_homeomorphic_to_disc:
- "simply_connected S \<longleftrightarrow> S = {} \<or> S homeomorphic ball (0::complex) 1" (is "?disc")
-proof -
- interpret SC_Chain
- using assms by (simp add: SC_Chain_def)
- have "?wn0 \<and> ?ci0 \<and> ?gp \<and> ?log \<and> ?sqrt \<and> ?bih \<and> ?disc"
-proof -
- have *: "\<lbrakk>\<alpha> \<Longrightarrow> \<beta>; \<beta> \<Longrightarrow> \<gamma>; \<gamma> \<Longrightarrow> \<delta>; \<delta> \<Longrightarrow> \<zeta>; \<zeta> \<Longrightarrow> \<eta>; \<eta> \<Longrightarrow> \<theta>; \<theta> \<Longrightarrow> \<xi>; \<xi> \<Longrightarrow> \<alpha>\<rbrakk>
- \<Longrightarrow> (\<alpha> \<longleftrightarrow> \<beta>) \<and> (\<alpha> \<longleftrightarrow> \<gamma>) \<and> (\<alpha> \<longleftrightarrow> \<delta>) \<and> (\<alpha> \<longleftrightarrow> \<zeta>) \<and>
- (\<alpha> \<longleftrightarrow> \<eta>) \<and> (\<alpha> \<longleftrightarrow> \<theta>) \<and> (\<alpha> \<longleftrightarrow> \<xi>)" for \<alpha> \<beta> \<gamma> \<delta> \<zeta> \<eta> \<theta> \<xi>
- by blast
- show ?thesis
- apply (rule *)
- using winding_number_zero apply metis
- using contour_integral_zero apply metis
- using global_primitive apply metis
- using holomorphic_log apply metis
- using holomorphic_sqrt apply simp
- using biholomorphic_to_disc apply blast
- using homeomorphic_to_disc apply blast
- using homeomorphic_to_disc_imp_simply_connected apply blast
- done
-qed
- then show ?wn0 ?ci0 ?gp ?log ?sqrt ?bih ?disc
- by safe
-qed
-
-corollary contractible_eq_simply_connected_2d:
- fixes S :: "complex set"
- shows "open S \<Longrightarrow> (contractible S \<longleftrightarrow> simply_connected S)"
- apply safe
- apply (simp add: contractible_imp_simply_connected)
- using convex_imp_contractible homeomorphic_contractible_eq simply_connected_eq_homeomorphic_to_disc by auto
-
-subsection\<open>A further chain of equivalences about components of the complement of a simply connected set\<close>
-
-text\<open>(following 1.35 in Burckel'S book)\<close>
-
-context SC_Chain
-begin
-
-lemma frontier_properties:
- assumes "simply_connected S"
- shows "if bounded S then connected(frontier S)
- else \<forall>C \<in> components(frontier S). \<not> bounded C"
-proof -
- have "S = {} \<or> S homeomorphic ball (0::complex) 1"
- using simply_connected_eq_homeomorphic_to_disc assms openS by blast
- then show ?thesis
- proof
- assume "S = {}"
- then have "bounded S"
- by simp
- with \<open>S = {}\<close> show ?thesis
- by simp
- next
- assume S01: "S homeomorphic ball (0::complex) 1"
- then obtain g f
- where gim: "g ` S = ball 0 1" and fg: "\<And>x. x \<in> S \<Longrightarrow> f(g x) = x"
- and fim: "f ` ball 0 1 = S" and gf: "\<And>y. cmod y < 1 \<Longrightarrow> g(f y) = y"
- and contg: "continuous_on S g" and contf: "continuous_on (ball 0 1) f"
- by (fastforce simp: homeomorphism_def homeomorphic_def)
- define D where "D \<equiv> \<lambda>n. ball (0::complex) (1 - 1/(of_nat n + 2))"
- define A where "A \<equiv> \<lambda>n. {z::complex. 1 - 1/(of_nat n + 2) < norm z \<and> norm z < 1}"
- define X where "X \<equiv> \<lambda>n::nat. closure(f ` A n)"
- have D01: "D n \<subseteq> ball 0 1" for n
- by (simp add: D_def ball_subset_ball_iff)
- have A01: "A n \<subseteq> ball 0 1" for n
- by (auto simp: A_def)
- have cloX: "closed(X n)" for n
- by (simp add: X_def)
- have Xsubclo: "X n \<subseteq> closure S" for n
- unfolding X_def by (metis A01 closure_mono fim image_mono)
- have connX: "connected(X n)" for n
- unfolding X_def
- apply (rule connected_imp_connected_closure)
- apply (rule connected_continuous_image)
- apply (simp add: continuous_on_subset [OF contf A01])
- using connected_annulus [of _ "0::complex"] by (simp add: A_def)
- have nestX: "X n \<subseteq> X m" if "m \<le> n" for m n
- proof -
- have "1 - 1 / (real m + 2) \<le> 1 - 1 / (real n + 2)"
- using that by (auto simp: field_simps)
- then show ?thesis
- by (auto simp: X_def A_def intro!: closure_mono)
- qed
- have "closure S - S \<subseteq> (\<Inter>n. X n)"
- proof
- fix x
- assume "x \<in> closure S - S"
- then have "x \<in> closure S" "x \<notin> S" by auto
- show "x \<in> (\<Inter>n. X n)"
- proof
- fix n
- have "ball 0 1 = closure (D n) \<union> A n"
- by (auto simp: D_def A_def le_less_trans)
- with fim have Seq: "S = f ` (closure (D n)) \<union> f ` (A n)"
- by (simp add: image_Un)
- have "continuous_on (closure (D n)) f"
- by (simp add: D_def cball_subset_ball_iff continuous_on_subset [OF contf])
- moreover have "compact (closure (D n))"
- by (simp add: D_def)
- ultimately have clo_fim: "closed (f ` closure (D n))"
- using compact_continuous_image compact_imp_closed by blast
- have *: "(f ` cball 0 (1 - 1 / (real n + 2))) \<subseteq> S"
- by (force simp: D_def Seq)
- show "x \<in> X n"
- using \<open>x \<in> closure S\<close> unfolding X_def Seq
- using \<open>x \<notin> S\<close> * D_def clo_fim by auto
- qed
- qed
- moreover have "(\<Inter>n. X n) \<subseteq> closure S - S"
- proof -
- have "(\<Inter>n. X n) \<subseteq> closure S"
- proof -
- have "(\<Inter>n. X n) \<subseteq> X 0"
- by blast
- also have "... \<subseteq> closure S"
- apply (simp add: X_def fim [symmetric])
- apply (rule closure_mono)
- by (auto simp: A_def)
- finally show "(\<Inter>n. X n) \<subseteq> closure S" .
- qed
- moreover have "(\<Inter>n. X n) \<inter> S \<subseteq> {}"
- proof (clarify, clarsimp simp: X_def fim [symmetric])
- fix x assume x [rule_format]: "\<forall>n. f x \<in> closure (f ` A n)" and "cmod x < 1"
- then obtain n where n: "1 / (1 - norm x) < of_nat n"
- using reals_Archimedean2 by blast
- with \<open>cmod x < 1\<close> gr0I have XX: "1 / of_nat n < 1 - norm x" and "n > 0"
- by (fastforce simp: field_split_simps algebra_simps)+
- have "f x \<in> f ` (D n)"
- using n \<open>cmod x < 1\<close> by (auto simp: field_split_simps algebra_simps D_def)
- moreover have " f ` D n \<inter> closure (f ` A n) = {}"
- proof -
- have op_fDn: "open(f ` (D n))"
- proof (rule invariance_of_domain)
- show "continuous_on (D n) f"
- by (rule continuous_on_subset [OF contf D01])
- show "open (D n)"
- by (simp add: D_def)
- show "inj_on f (D n)"
- unfolding inj_on_def using D01 by (metis gf mem_ball_0 subsetCE)
- qed
- have injf: "inj_on f (ball 0 1)"
- by (metis mem_ball_0 inj_on_def gf)
- have "D n \<union> A n \<subseteq> ball 0 1"
- using D01 A01 by simp
- moreover have "D n \<inter> A n = {}"
- by (auto simp: D_def A_def)
- ultimately have "f ` D n \<inter> f ` A n = {}"
- by (metis A01 D01 image_is_empty inj_on_image_Int injf)
- then show ?thesis
- by (simp add: open_Int_closure_eq_empty [OF op_fDn])
- qed
- ultimately show False
- using x [of n] by blast
- qed
- ultimately
- show "(\<Inter>n. X n) \<subseteq> closure S - S"
- using closure_subset disjoint_iff_not_equal by blast
- qed
- ultimately have "closure S - S = (\<Inter>n. X n)" by blast
- then have frontierS: "frontier S = (\<Inter>n. X n)"
- by (simp add: frontier_def openS interior_open)
- show ?thesis
- proof (cases "bounded S")
- case True
- have bouX: "bounded (X n)" for n
- apply (simp add: X_def)
- apply (rule bounded_closure)
- by (metis A01 fim image_mono bounded_subset [OF True])
- have compaX: "compact (X n)" for n
- apply (simp add: compact_eq_bounded_closed bouX)
- apply (auto simp: X_def)
- done
- have "connected (\<Inter>n. X n)"
- by (metis nestX compaX connX connected_nest)
- then show ?thesis
- by (simp add: True \<open>frontier S = (\<Inter>n. X n)\<close>)
- next
- case False
- have unboundedX: "\<not> bounded(X n)" for n
- proof
- assume bXn: "bounded(X n)"
- have "continuous_on (cball 0 (1 - 1 / (2 + real n))) f"
- by (simp add: cball_subset_ball_iff continuous_on_subset [OF contf])
- then have "bounded (f ` cball 0 (1 - 1 / (2 + real n)))"
- by (simp add: compact_imp_bounded [OF compact_continuous_image])
- moreover have "bounded (f ` A n)"
- by (auto simp: X_def closure_subset image_subset_iff bounded_subset [OF bXn])
- ultimately have "bounded (f ` (cball 0 (1 - 1/(2 + real n)) \<union> A n))"
- by (simp add: image_Un)
- then have "bounded (f ` ball 0 1)"
- apply (rule bounded_subset)
- apply (auto simp: A_def algebra_simps)
- done
- then show False
- using False by (simp add: fim [symmetric])
- qed
- have clo_INTX: "closed(\<Inter>(range X))"
- by (metis cloX closed_INT)
- then have lcX: "locally compact (\<Inter>(range X))"
- by (metis closed_imp_locally_compact)
- have False if C: "C \<in> components (frontier S)" and boC: "bounded C" for C
- proof -
- have "closed C"
- by (metis C closed_components frontier_closed)
- then have "compact C"
- by (metis boC compact_eq_bounded_closed)
- have Cco: "C \<in> components (\<Inter>(range X))"
- by (metis frontierS C)
- obtain K where "C \<subseteq> K" "compact K"
- and Ksub: "K \<subseteq> \<Inter>(range X)" and clo: "closed(\<Inter>(range X) - K)"
- proof (cases "{k. C \<subseteq> k \<and> compact k \<and> openin (top_of_set (\<Inter>(range X))) k} = {}")
- case True
- then show ?thesis
- using Sura_Bura [OF lcX Cco \<open>compact C\<close>] boC
- by (simp add: True)
- next
- case False
- then obtain L where "compact L" "C \<subseteq> L" and K: "openin (top_of_set (\<Inter>x. X x)) L"
- by blast
- show ?thesis
- proof
- show "L \<subseteq> \<Inter>(range X)"
- by (metis K openin_imp_subset)
- show "closed (\<Inter>(range X) - L)"
- by (metis closedin_diff closedin_self closedin_closed_trans [OF _ clo_INTX] K)
- qed (use \<open>compact L\<close> \<open>C \<subseteq> L\<close> in auto)
- qed
- obtain U V where "open U" and "compact (closure U)" and "open V" "K \<subseteq> U"
- and V: "\<Inter>(range X) - K \<subseteq> V" and "U \<inter> V = {}"
- using separation_normal_compact [OF \<open>compact K\<close> clo] by blast
- then have "U \<inter> (\<Inter> (range X) - K) = {}"
- by blast
- have "(closure U - U) \<inter> (\<Inter>n. X n \<inter> closure U) \<noteq> {}"
- proof (rule compact_imp_fip)
- show "compact (closure U - U)"
- by (metis \<open>compact (closure U)\<close> \<open>open U\<close> compact_diff)
- show "\<And>T. T \<in> range (\<lambda>n. X n \<inter> closure U) \<Longrightarrow> closed T"
- by clarify (metis cloX closed_Int closed_closure)
- show "(closure U - U) \<inter> \<Inter>\<F> \<noteq> {}"
- if "finite \<F>" and \<F>: "\<F> \<subseteq> range (\<lambda>n. X n \<inter> closure U)" for \<F>
- proof
- assume empty: "(closure U - U) \<inter> \<Inter>\<F> = {}"
- obtain J where "finite J" and J: "\<F> = (\<lambda>n. X n \<inter> closure U) ` J"
- using finite_subset_image [OF \<open>finite \<F>\<close> \<F>] by auto
- show False
- proof (cases "J = {}")
- case True
- with J empty have "closed U"
- by (simp add: closure_subset_eq)
- have "C \<noteq> {}"
- using C in_components_nonempty by blast
- then have "U \<noteq> {}"
- using \<open>K \<subseteq> U\<close> \<open>C \<subseteq> K\<close> by blast
- moreover have "U \<noteq> UNIV"
- using \<open>compact (closure U)\<close> by auto
- ultimately show False
- using \<open>open U\<close> \<open>closed U\<close> clopen by blast
- next
- case False
- define j where "j \<equiv> Max J"
- have "j \<in> J"
- by (simp add: False \<open>finite J\<close> j_def)
- have jmax: "\<And>m. m \<in> J \<Longrightarrow> m \<le> j"
- by (simp add: j_def \<open>finite J\<close>)
- have "\<Inter> ((\<lambda>n. X n \<inter> closure U) ` J) = X j \<inter> closure U"
- using False jmax nestX \<open>j \<in> J\<close> by auto
- then have "X j \<inter> closure U = X j \<inter> U"
- apply safe
- using DiffI J empty apply auto[1]
- using closure_subset by blast
- then have "openin (top_of_set (X j)) (X j \<inter> closure U)"
- by (simp add: openin_open_Int \<open>open U\<close>)
- moreover have "closedin (top_of_set (X j)) (X j \<inter> closure U)"
- by (simp add: closedin_closed_Int)
- moreover have "X j \<inter> closure U \<noteq> X j"
- by (metis unboundedX \<open>compact (closure U)\<close> bounded_subset compact_eq_bounded_closed inf.order_iff)
- moreover have "X j \<inter> closure U \<noteq> {}"
- proof -
- have "C \<noteq> {}"
- using C in_components_nonempty by blast
- moreover have "C \<subseteq> X j \<inter> closure U"
- using \<open>C \<subseteq> K\<close> \<open>K \<subseteq> U\<close> Ksub closure_subset by blast
- ultimately show ?thesis by blast
- qed
- ultimately show False
- using connX [of j] by (force simp: connected_clopen)
- qed
- qed
- qed
- moreover have "(\<Inter>n. X n \<inter> closure U) = (\<Inter>n. X n) \<inter> closure U"
- by blast
- moreover have "x \<in> U" if "\<And>n. x \<in> X n" "x \<in> closure U" for x
- proof -
- have "x \<notin> V"
- using \<open>U \<inter> V = {}\<close> \<open>open V\<close> closure_iff_nhds_not_empty that(2) by blast
- then show ?thesis
- by (metis (no_types) Diff_iff INT_I V \<open>K \<subseteq> U\<close> contra_subsetD that(1))
- qed
- ultimately show False
- by (auto simp: open_Int_closure_eq_empty [OF \<open>open V\<close>, of U])
- qed
- then show ?thesis
- by (auto simp: False)
- qed
- qed
-qed
-
-
-lemma unbounded_complement_components:
- assumes C: "C \<in> components (- S)" and S: "connected S"
- and prev: "if bounded S then connected(frontier S)
- else \<forall>C \<in> components(frontier S). \<not> bounded C"
- shows "\<not> bounded C"
-proof (cases "bounded S")
- case True
- with prev have "S \<noteq> UNIV" and confr: "connected(frontier S)"
- by auto
- obtain w where C_ccsw: "C = connected_component_set (- S) w" and "w \<notin> S"
- using C by (auto simp: components_def)
- show ?thesis
- proof (cases "S = {}")
- case True with C show ?thesis by auto
- next
- case False
- show ?thesis
- proof
- assume "bounded C"
- then have "outside C \<noteq> {}"
- using outside_bounded_nonempty by metis
- then obtain z where z: "\<not> bounded (connected_component_set (- C) z)" and "z \<notin> C"
- by (auto simp: outside_def)
- have clo_ccs: "closed (connected_component_set (- S) x)" for x
- by (simp add: closed_Compl closed_connected_component openS)
- have "connected_component_set (- S) w = connected_component_set (- S) z"
- proof (rule joinable_connected_component_eq [OF confr])
- show "frontier S \<subseteq> - S"
- using openS by (auto simp: frontier_def interior_open)
- have False if "connected_component_set (- S) w \<inter> frontier (- S) = {}"
- proof -
- have "C \<inter> frontier S = {}"
- using that by (simp add: C_ccsw)
- then show False
- by (metis C_ccsw ComplI Compl_eq_Compl_iff Diff_subset False \<open>w \<notin> S\<close> clo_ccs closure_closed compl_bot_eq connected_component_eq_UNIV connected_component_eq_empty empty_subsetI frontier_complement frontier_def frontier_not_empty frontier_of_connected_component_subset le_inf_iff subset_antisym)
- qed
- then show "connected_component_set (- S) w \<inter> frontier S \<noteq> {}"
- by auto
- have *: "\<lbrakk>frontier C \<subseteq> C; frontier C \<subseteq> F; frontier C \<noteq> {}\<rbrakk> \<Longrightarrow> C \<inter> F \<noteq> {}" for C F::"complex set"
- by blast
- have "connected_component_set (- S) z \<inter> frontier (- S) \<noteq> {}"
- proof (rule *)
- show "frontier (connected_component_set (- S) z) \<subseteq> connected_component_set (- S) z"
- by (auto simp: closed_Compl closed_connected_component frontier_def openS)
- show "frontier (connected_component_set (- S) z) \<subseteq> frontier (- S)"
- using frontier_of_connected_component_subset by fastforce
- have "\<not> bounded (-S)"
- by (simp add: True cobounded_imp_unbounded)
- then have "connected_component_set (- S) z \<noteq> {}"
- apply (simp only: connected_component_eq_empty)
- using confr openS \<open>bounded C\<close> \<open>w \<notin> S\<close>
- apply (simp add: frontier_def interior_open C_ccsw)
- by (metis ComplI Compl_eq_Diff_UNIV connected_UNIV closed_closure closure_subset connected_component_eq_self
- connected_diff_open_from_closed subset_UNIV)
- then show "frontier (connected_component_set (- S) z) \<noteq> {}"
- apply (simp add: frontier_eq_empty connected_component_eq_UNIV)
- apply (metis False compl_top_eq double_compl)
- done
- qed
- then show "connected_component_set (- S) z \<inter> frontier S \<noteq> {}"
- by auto
- qed
- then show False
- by (metis C_ccsw Compl_iff \<open>w \<notin> S\<close> \<open>z \<notin> C\<close> connected_component_eq_empty connected_component_idemp)
- qed
- qed
-next
- case False
- obtain w where C_ccsw: "C = connected_component_set (- S) w" and "w \<notin> S"
- using C by (auto simp: components_def)
- have "frontier (connected_component_set (- S) w) \<subseteq> connected_component_set (- S) w"
- by (simp add: closed_Compl closed_connected_component frontier_subset_eq openS)
- moreover have "frontier (connected_component_set (- S) w) \<subseteq> frontier S"
- using frontier_complement frontier_of_connected_component_subset by blast
- moreover have "frontier (connected_component_set (- S) w) \<noteq> {}"
- by (metis C C_ccsw False bounded_empty compl_top_eq connected_component_eq_UNIV double_compl frontier_not_empty in_components_nonempty)
- ultimately obtain z where zin: "z \<in> frontier S" and z: "z \<in> connected_component_set (- S) w"
- by blast
- have *: "connected_component_set (frontier S) z \<in> components(frontier S)"
- by (simp add: \<open>z \<in> frontier S\<close> componentsI)
- with prev False have "\<not> bounded (connected_component_set (frontier S) z)"
- by simp
- moreover have "connected_component (- S) w = connected_component (- S) z"
- using connected_component_eq [OF z] by force
- ultimately show ?thesis
- by (metis C_ccsw * zin bounded_subset closed_Compl closure_closed connected_component_maximal
- connected_component_refl connected_connected_component frontier_closures in_components_subset le_inf_iff mem_Collect_eq openS)
-qed
-
-lemma empty_inside:
- assumes "connected S" "\<And>C. C \<in> components (- S) \<Longrightarrow> \<not> bounded C"
- shows "inside S = {}"
- using assms by (auto simp: components_def inside_def)
-
-lemma empty_inside_imp_simply_connected:
- "\<lbrakk>connected S; inside S = {}\<rbrakk> \<Longrightarrow> simply_connected S"
- by (metis ComplI inside_Un_outside openS outside_mono simply_connected_eq_winding_number_zero subsetCE sup_bot.left_neutral winding_number_zero_in_outside)
-
-end
-
-proposition
- fixes S :: "complex set"
- assumes "open S"
- shows simply_connected_eq_frontier_properties:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (if bounded S then connected(frontier S)
- else (\<forall>C \<in> components(frontier S). \<not>bounded C))" (is "?fp")
- and simply_connected_eq_unbounded_complement_components:
- "simply_connected S \<longleftrightarrow>
- connected S \<and> (\<forall>C \<in> components(- S). \<not>bounded C)" (is "?ucc")
- and simply_connected_eq_empty_inside:
- "simply_connected S \<longleftrightarrow>
- connected S \<and> inside S = {}" (is "?ei")
-proof -
- interpret SC_Chain
- using assms by (simp add: SC_Chain_def)
- have "?fp \<and> ?ucc \<and> ?ei"
-proof -
- have *: "\<lbrakk>\<alpha> \<Longrightarrow> \<beta>; \<beta> \<Longrightarrow> \<gamma>; \<gamma> \<Longrightarrow> \<delta>; \<delta> \<Longrightarrow> \<alpha>\<rbrakk>
- \<Longrightarrow> (\<alpha> \<longleftrightarrow> \<beta>) \<and> (\<alpha> \<longleftrightarrow> \<gamma>) \<and> (\<alpha> \<longleftrightarrow> \<delta>)" for \<alpha> \<beta> \<gamma> \<delta>
- by blast
- show ?thesis
- apply (rule *)
- using frontier_properties simply_connected_imp_connected apply blast
-apply clarify
- using unbounded_complement_components simply_connected_imp_connected apply blast
- using empty_inside apply blast
- using empty_inside_imp_simply_connected apply blast
- done
-qed
- then show ?fp ?ucc ?ei
- by safe
-qed
-
-lemma simply_connected_iff_simple:
- fixes S :: "complex set"
- assumes "open S" "bounded S"
- shows "simply_connected S \<longleftrightarrow> connected S \<and> connected(- S)"
- apply (simp add: simply_connected_eq_unbounded_complement_components assms, safe)
- apply (metis DIM_complex assms(2) cobounded_has_bounded_component double_compl order_refl)
- by (meson assms inside_bounded_complement_connected_empty simply_connected_eq_empty_inside simply_connected_eq_unbounded_complement_components)
-
-subsection\<open>Further equivalences based on continuous logs and sqrts\<close>
-
-context SC_Chain
-begin
-
-lemma continuous_log:
- fixes f :: "complex\<Rightarrow>complex"
- assumes S: "simply_connected S"
- and contf: "continuous_on S f" and nz: "\<And>z. z \<in> S \<Longrightarrow> f z \<noteq> 0"
- shows "\<exists>g. continuous_on S g \<and> (\<forall>z \<in> S. f z = exp(g z))"
-proof -
- consider "S = {}" | "S homeomorphic ball (0::complex) 1"
- using simply_connected_eq_homeomorphic_to_disc [OF openS] S by metis
- then show ?thesis
- proof cases
- case 1 then show ?thesis
- by simp
- next
- case 2
- then obtain h k :: "complex\<Rightarrow>complex"
- where kh: "\<And>x. x \<in> S \<Longrightarrow> k(h x) = x" and him: "h ` S = ball 0 1"
- and conth: "continuous_on S h"
- and hk: "\<And>y. y \<in> ball 0 1 \<Longrightarrow> h(k y) = y" and kim: "k ` ball 0 1 = S"
- and contk: "continuous_on (ball 0 1) k"
- unfolding homeomorphism_def homeomorphic_def by metis
- obtain g where contg: "continuous_on (ball 0 1) g"
- and expg: "\<And>z. z \<in> ball 0 1 \<Longrightarrow> (f \<circ> k) z = exp (g z)"
- proof (rule continuous_logarithm_on_ball)
- show "continuous_on (ball 0 1) (f \<circ> k)"
- apply (rule continuous_on_compose [OF contk])
- using kim continuous_on_subset [OF contf]
- by blast
- show "\<And>z. z \<in> ball 0 1 \<Longrightarrow> (f \<circ> k) z \<noteq> 0"
- using kim nz by auto
- qed auto
- then show ?thesis
- by (metis comp_apply conth continuous_on_compose him imageI kh)
- qed
-qed
-
-lemma continuous_sqrt:
- fixes f :: "complex\<Rightarrow>complex"
- assumes contf: "continuous_on S f" and nz: "\<And>z. z \<in> S \<Longrightarrow> f z \<noteq> 0"
- and prev: "\<And>f::complex\<Rightarrow>complex.
- \<lbrakk>continuous_on S f; \<And>z. z \<in> S \<Longrightarrow> f z \<noteq> 0\<rbrakk>
- \<Longrightarrow> \<exists>g. continuous_on S g \<and> (\<forall>z \<in> S. f z = exp(g z))"
- shows "\<exists>g. continuous_on S g \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)"
-proof -
- obtain g where contg: "continuous_on S g" and geq: "\<And>z. z \<in> S \<Longrightarrow> f z = exp(g z)"
- using contf nz prev by metis
- show ?thesis
-proof (intro exI ballI conjI)
- show "continuous_on S (\<lambda>z. exp(g z/2))"
- by (intro continuous_intros) (auto simp: contg)
- show "\<And>z. z \<in> S \<Longrightarrow> f z = (exp (g z/2))\<^sup>2"
- by (metis (no_types, lifting) divide_inverse exp_double geq mult.left_commute mult.right_neutral right_inverse zero_neq_numeral)
- qed
-qed
-
-lemma continuous_sqrt_imp_simply_connected:
- assumes "connected S"
- and prev: "\<And>f::complex\<Rightarrow>complex. \<lbrakk>continuous_on S f; \<forall>z \<in> S. f z \<noteq> 0\<rbrakk>
- \<Longrightarrow> \<exists>g. continuous_on S g \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)"
- shows "simply_connected S"
-proof (clarsimp simp add: simply_connected_eq_holomorphic_sqrt [OF openS] \<open>connected S\<close>)
- fix f
- assume "f holomorphic_on S" and nz: "\<forall>z\<in>S. f z \<noteq> 0"
- then obtain g where contg: "continuous_on S g" and geq: "\<And>z. z \<in> S \<Longrightarrow> f z = (g z)\<^sup>2"
- by (metis holomorphic_on_imp_continuous_on prev)
- show "\<exists>g. g holomorphic_on S \<and> (\<forall>z\<in>S. f z = (g z)\<^sup>2)"
- proof (intro exI ballI conjI)
- show "g holomorphic_on S"
- proof (clarsimp simp add: holomorphic_on_open [OF openS])
- fix z
- assume "z \<in> S"
- with nz geq have "g z \<noteq> 0"
- by auto
- obtain \<delta> where "0 < \<delta>" "\<And>w. \<lbrakk>w \<in> S; dist w z < \<delta>\<rbrakk> \<Longrightarrow> dist (g w) (g z) < cmod (g z)"
- using contg [unfolded continuous_on_iff] by (metis \<open>g z \<noteq> 0\<close> \<open>z \<in> S\<close> zero_less_norm_iff)
- then have \<delta>: "\<And>w. \<lbrakk>w \<in> S; w \<in> ball z \<delta>\<rbrakk> \<Longrightarrow> g w + g z \<noteq> 0"
- apply (clarsimp simp: dist_norm)
- by (metis \<open>g z \<noteq> 0\<close> add_diff_cancel_left' diff_0_right norm_eq_zero norm_increases_online norm_minus_commute norm_not_less_zero not_less_iff_gr_or_eq)
- have *: "(\<lambda>x. (f x - f z) / (x - z) / (g x + g z)) \<midarrow>z\<rightarrow> deriv f z / (g z + g z)"
- apply (intro tendsto_intros)
- using SC_Chain.openS SC_Chain_axioms \<open>f holomorphic_on S\<close> \<open>z \<in> S\<close> has_field_derivativeD holomorphic_derivI apply fastforce
- using \<open>z \<in> S\<close> contg continuous_on_eq_continuous_at isCont_def openS apply blast
- by (simp add: \<open>g z \<noteq> 0\<close>)
- then have "(g has_field_derivative deriv f z / (g z + g z)) (at z)"
- unfolding has_field_derivative_iff
- proof (rule Lim_transform_within_open)
- show "open (ball z \<delta> \<inter> S)"
- by (simp add: openS open_Int)
- show "z \<in> ball z \<delta> \<inter> S"
- using \<open>z \<in> S\<close> \<open>0 < \<delta>\<close> by simp
- show "\<And>x. \<lbrakk>x \<in> ball z \<delta> \<inter> S; x \<noteq> z\<rbrakk>
- \<Longrightarrow> (f x - f z) / (x - z) / (g x + g z) = (g x - g z) / (x - z)"
- using \<delta>
- apply (simp add: geq \<open>z \<in> S\<close> divide_simps)
- apply (auto simp: algebra_simps power2_eq_square)
- done
- qed
- then show "\<exists>f'. (g has_field_derivative f') (at z)" ..
- qed
- qed (use geq in auto)
-qed
-
-end
-
-proposition
- fixes S :: "complex set"
- assumes "open S"
- shows simply_connected_eq_continuous_log:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>f::complex\<Rightarrow>complex. continuous_on S f \<and> (\<forall>z \<in> S. f z \<noteq> 0)
- \<longrightarrow> (\<exists>g. continuous_on S g \<and> (\<forall>z \<in> S. f z = exp (g z))))" (is "?log")
- and simply_connected_eq_continuous_sqrt:
- "simply_connected S \<longleftrightarrow>
- connected S \<and>
- (\<forall>f::complex\<Rightarrow>complex. continuous_on S f \<and> (\<forall>z \<in> S. f z \<noteq> 0)
- \<longrightarrow> (\<exists>g. continuous_on S g \<and> (\<forall>z \<in> S. f z = (g z)\<^sup>2)))" (is "?sqrt")
-proof -
- interpret SC_Chain
- using assms by (simp add: SC_Chain_def)
- have "?log \<and> ?sqrt"
-proof -
- have *: "\<lbrakk>\<alpha> \<Longrightarrow> \<beta>; \<beta> \<Longrightarrow> \<gamma>; \<gamma> \<Longrightarrow> \<alpha>\<rbrakk>
- \<Longrightarrow> (\<alpha> \<longleftrightarrow> \<beta>) \<and> (\<alpha> \<longleftrightarrow> \<gamma>)" for \<alpha> \<beta> \<gamma>
- by blast
- show ?thesis
- apply (rule *)
- apply (simp add: local.continuous_log winding_number_zero)
- apply (simp add: continuous_sqrt)
- apply (simp add: continuous_sqrt_imp_simply_connected)
- done
-qed
- then show ?log ?sqrt
- by safe
-qed
-
-
-subsection\<^marker>\<open>tag unimportant\<close> \<open>More Borsukian results\<close>
-
-lemma Borsukian_componentwise_eq:
- fixes S :: "'a::euclidean_space set"
- assumes S: "locally connected S \<or> compact S"
- shows "Borsukian S \<longleftrightarrow> (\<forall>C \<in> components S. Borsukian C)"
-proof -
- have *: "ANR(-{0::complex})"
- by (simp add: ANR_delete open_Compl open_imp_ANR)
- show ?thesis
- using cohomotopically_trivial_on_components [OF assms *] by (auto simp: Borsukian_alt)
-qed
-
-lemma Borsukian_componentwise:
- fixes S :: "'a::euclidean_space set"
- assumes "locally connected S \<or> compact S" "\<And>C. C \<in> components S \<Longrightarrow> Borsukian C"
- shows "Borsukian S"
- by (metis Borsukian_componentwise_eq assms)
-
-lemma simply_connected_eq_Borsukian:
- fixes S :: "complex set"
- shows "open S \<Longrightarrow> (simply_connected S \<longleftrightarrow> connected S \<and> Borsukian S)"
- by (auto simp: simply_connected_eq_continuous_log Borsukian_continuous_logarithm)
-
-lemma Borsukian_eq_simply_connected:
- fixes S :: "complex set"
- shows "open S \<Longrightarrow> Borsukian S \<longleftrightarrow> (\<forall>C \<in> components S. simply_connected C)"
-apply (auto simp: Borsukian_componentwise_eq open_imp_locally_connected)
- using in_components_connected open_components simply_connected_eq_Borsukian apply blast
- using open_components simply_connected_eq_Borsukian by blast
-
-lemma Borsukian_separation_open_closed:
- fixes S :: "complex set"
- assumes S: "open S \<or> closed S" and "bounded S"
- shows "Borsukian S \<longleftrightarrow> connected(- S)"
- using S
-proof
- assume "open S"
- show ?thesis
- unfolding Borsukian_eq_simply_connected [OF \<open>open S\<close>]
- by (meson \<open>open S\<close> \<open>bounded S\<close> bounded_subset in_components_connected in_components_subset nonseparation_by_component_eq open_components simply_connected_iff_simple)
-next
- assume "closed S"
- with \<open>bounded S\<close> show ?thesis
- by (simp add: Borsukian_separation_compact compact_eq_bounded_closed)
-qed
-
-
-subsection\<open>Finally, the Riemann Mapping Theorem\<close>
-
-theorem Riemann_mapping_theorem:
- "open S \<and> simply_connected S \<longleftrightarrow>
- S = {} \<or> S = UNIV \<or>
- (\<exists>f g. f holomorphic_on S \<and> g holomorphic_on ball 0 1 \<and>
- (\<forall>z \<in> S. f z \<in> ball 0 1 \<and> g(f z) = z) \<and>
- (\<forall>z \<in> ball 0 1. g z \<in> S \<and> f(g z) = z))"
- (is "_ = ?rhs")
-proof -
- have "simply_connected S \<longleftrightarrow> ?rhs" if "open S"
- by (simp add: simply_connected_eq_biholomorphic_to_disc that)
- moreover have "open S" if "?rhs"
- proof -
- { fix f g
- assume g: "g holomorphic_on ball 0 1" "\<forall>z\<in>ball 0 1. g z \<in> S \<and> f (g z) = z"
- and "\<forall>z\<in>S. cmod (f z) < 1 \<and> g (f z) = z"
- then have "S = g ` (ball 0 1)"
- by (force simp:)
- then have "open S"
- by (metis open_ball g inj_on_def open_mapping_thm3)
- }
- with that show "open S" by auto
- qed
- ultimately show ?thesis by metis
-qed
-
-end