src/HOL/NthRoot.thy
author wenzelm
Mon Mar 16 18:24:30 2009 +0100 (2009-03-16)
changeset 30549 d2d7874648bd
parent 30273 ecd6f0ca62ea
child 31014 79f0858d9d49
permissions -rw-r--r--
simplified method setup;
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(*  Title       : NthRoot.thy
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    Author      : Jacques D. Fleuriot
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    Copyright   : 1998  University of Cambridge
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    Conversion to Isar and new proofs by Lawrence C Paulson, 2004
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*)
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header {* Nth Roots of Real Numbers *}
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theory NthRoot
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imports Parity Deriv
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begin
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subsection {* Existence of Nth Root *}
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text {* Existence follows from the Intermediate Value Theorem *}
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lemma realpow_pos_nth:
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  assumes n: "0 < n"
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  assumes a: "0 < a"
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  shows "\<exists>r>0. r ^ n = (a::real)"
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proof -
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  have "\<exists>r\<ge>0. r \<le> (max 1 a) \<and> r ^ n = a"
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  proof (rule IVT)
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    show "0 ^ n \<le> a" using n a by (simp add: power_0_left)
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    show "0 \<le> max 1 a" by simp
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    from n have n1: "1 \<le> n" by simp
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    have "a \<le> max 1 a ^ 1" by simp
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    also have "max 1 a ^ 1 \<le> max 1 a ^ n"
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      using n1 by (rule power_increasing, simp)
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    finally show "a \<le> max 1 a ^ n" .
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    show "\<forall>r. 0 \<le> r \<and> r \<le> max 1 a \<longrightarrow> isCont (\<lambda>x. x ^ n) r"
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      by (simp add: isCont_power)
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  qed
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  then obtain r where r: "0 \<le> r \<and> r ^ n = a" by fast
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  with n a have "r \<noteq> 0" by (auto simp add: power_0_left)
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  with r have "0 < r \<and> r ^ n = a" by simp
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  thus ?thesis ..
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qed
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(* Used by Integration/RealRandVar.thy in AFP *)
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lemma realpow_pos_nth2: "(0::real) < a \<Longrightarrow> \<exists>r>0. r ^ Suc n = a"
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by (blast intro: realpow_pos_nth)
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text {* Uniqueness of nth positive root *}
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lemma realpow_pos_nth_unique:
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  "\<lbrakk>0 < n; 0 < a\<rbrakk> \<Longrightarrow> \<exists>!r. 0 < r \<and> r ^ n = (a::real)"
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apply (auto intro!: realpow_pos_nth)
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apply (rule_tac n=n in power_eq_imp_eq_base, simp_all)
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done
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subsection {* Nth Root *}
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text {* We define roots of negative reals such that
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  @{term "root n (- x) = - root n x"}. This allows
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  us to omit side conditions from many theorems. *}
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definition
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  root :: "[nat, real] \<Rightarrow> real" where
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  "root n x = (if 0 < x then (THE u. 0 < u \<and> u ^ n = x) else
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               if x < 0 then - (THE u. 0 < u \<and> u ^ n = - x) else 0)"
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lemma real_root_zero [simp]: "root n 0 = 0"
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unfolding root_def by simp
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lemma real_root_minus: "0 < n \<Longrightarrow> root n (- x) = - root n x"
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unfolding root_def by simp
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lemma real_root_gt_zero: "\<lbrakk>0 < n; 0 < x\<rbrakk> \<Longrightarrow> 0 < root n x"
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apply (simp add: root_def)
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apply (drule (1) realpow_pos_nth_unique)
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apply (erule theI' [THEN conjunct1])
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done
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lemma real_root_pow_pos: (* TODO: rename *)
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  "\<lbrakk>0 < n; 0 < x\<rbrakk> \<Longrightarrow> root n x ^ n = x"
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apply (simp add: root_def)
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apply (drule (1) realpow_pos_nth_unique)
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apply (erule theI' [THEN conjunct2])
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done
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lemma real_root_pow_pos2 [simp]: (* TODO: rename *)
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  "\<lbrakk>0 < n; 0 \<le> x\<rbrakk> \<Longrightarrow> root n x ^ n = x"
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by (auto simp add: order_le_less real_root_pow_pos)
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lemma odd_real_root_pow: "odd n \<Longrightarrow> root n x ^ n = x"
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apply (rule_tac x=0 and y=x in linorder_le_cases)
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apply (erule (1) real_root_pow_pos2 [OF odd_pos])
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apply (subgoal_tac "root n (- x) ^ n = - x")
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apply (simp add: real_root_minus odd_pos)
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apply (simp add: odd_pos)
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done
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lemma real_root_ge_zero: "\<lbrakk>0 < n; 0 \<le> x\<rbrakk> \<Longrightarrow> 0 \<le> root n x"
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by (auto simp add: order_le_less real_root_gt_zero)
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lemma real_root_power_cancel: "\<lbrakk>0 < n; 0 \<le> x\<rbrakk> \<Longrightarrow> root n (x ^ n) = x"
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apply (subgoal_tac "0 \<le> x ^ n")
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apply (subgoal_tac "0 \<le> root n (x ^ n)")
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apply (subgoal_tac "root n (x ^ n) ^ n = x ^ n")
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apply (erule (3) power_eq_imp_eq_base)
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apply (erule (1) real_root_pow_pos2)
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apply (erule (1) real_root_ge_zero)
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apply (erule zero_le_power)
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done
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lemma odd_real_root_power_cancel: "odd n \<Longrightarrow> root n (x ^ n) = x"
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apply (rule_tac x=0 and y=x in linorder_le_cases)
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apply (erule (1) real_root_power_cancel [OF odd_pos])
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apply (subgoal_tac "root n ((- x) ^ n) = - x")
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apply (simp add: real_root_minus odd_pos)
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apply (erule real_root_power_cancel [OF odd_pos], simp)
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done
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lemma real_root_pos_unique:
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  "\<lbrakk>0 < n; 0 \<le> y; y ^ n = x\<rbrakk> \<Longrightarrow> root n x = y"
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by (erule subst, rule real_root_power_cancel)
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lemma odd_real_root_unique:
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  "\<lbrakk>odd n; y ^ n = x\<rbrakk> \<Longrightarrow> root n x = y"
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by (erule subst, rule odd_real_root_power_cancel)
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lemma real_root_one [simp]: "0 < n \<Longrightarrow> root n 1 = 1"
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by (simp add: real_root_pos_unique)
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text {* Root function is strictly monotonic, hence injective *}
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lemma real_root_less_mono_lemma:
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  "\<lbrakk>0 < n; 0 \<le> x; x < y\<rbrakk> \<Longrightarrow> root n x < root n y"
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apply (subgoal_tac "0 \<le> y")
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apply (subgoal_tac "root n x ^ n < root n y ^ n")
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apply (erule power_less_imp_less_base)
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apply (erule (1) real_root_ge_zero)
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apply simp
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apply simp
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done
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lemma real_root_less_mono: "\<lbrakk>0 < n; x < y\<rbrakk> \<Longrightarrow> root n x < root n y"
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apply (cases "0 \<le> x")
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apply (erule (2) real_root_less_mono_lemma)
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apply (cases "0 \<le> y")
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apply (rule_tac y=0 in order_less_le_trans)
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apply (subgoal_tac "0 < root n (- x)")
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apply (simp add: real_root_minus)
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apply (simp add: real_root_gt_zero)
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apply (simp add: real_root_ge_zero)
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apply (subgoal_tac "root n (- y) < root n (- x)")
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apply (simp add: real_root_minus)
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apply (simp add: real_root_less_mono_lemma)
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done
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lemma real_root_le_mono: "\<lbrakk>0 < n; x \<le> y\<rbrakk> \<Longrightarrow> root n x \<le> root n y"
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by (auto simp add: order_le_less real_root_less_mono)
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lemma real_root_less_iff [simp]:
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  "0 < n \<Longrightarrow> (root n x < root n y) = (x < y)"
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apply (cases "x < y")
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apply (simp add: real_root_less_mono)
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apply (simp add: linorder_not_less real_root_le_mono)
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done
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lemma real_root_le_iff [simp]:
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  "0 < n \<Longrightarrow> (root n x \<le> root n y) = (x \<le> y)"
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apply (cases "x \<le> y")
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apply (simp add: real_root_le_mono)
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apply (simp add: linorder_not_le real_root_less_mono)
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done
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lemma real_root_eq_iff [simp]:
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  "0 < n \<Longrightarrow> (root n x = root n y) = (x = y)"
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by (simp add: order_eq_iff)
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lemmas real_root_gt_0_iff [simp] = real_root_less_iff [where x=0, simplified]
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lemmas real_root_lt_0_iff [simp] = real_root_less_iff [where y=0, simplified]
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lemmas real_root_ge_0_iff [simp] = real_root_le_iff [where x=0, simplified]
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lemmas real_root_le_0_iff [simp] = real_root_le_iff [where y=0, simplified]
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lemmas real_root_eq_0_iff [simp] = real_root_eq_iff [where y=0, simplified]
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lemma real_root_gt_1_iff [simp]: "0 < n \<Longrightarrow> (1 < root n y) = (1 < y)"
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by (insert real_root_less_iff [where x=1], simp)
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lemma real_root_lt_1_iff [simp]: "0 < n \<Longrightarrow> (root n x < 1) = (x < 1)"
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by (insert real_root_less_iff [where y=1], simp)
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lemma real_root_ge_1_iff [simp]: "0 < n \<Longrightarrow> (1 \<le> root n y) = (1 \<le> y)"
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by (insert real_root_le_iff [where x=1], simp)
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lemma real_root_le_1_iff [simp]: "0 < n \<Longrightarrow> (root n x \<le> 1) = (x \<le> 1)"
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by (insert real_root_le_iff [where y=1], simp)
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lemma real_root_eq_1_iff [simp]: "0 < n \<Longrightarrow> (root n x = 1) = (x = 1)"
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by (insert real_root_eq_iff [where y=1], simp)
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text {* Roots of roots *}
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lemma real_root_Suc_0 [simp]: "root (Suc 0) x = x"
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by (simp add: odd_real_root_unique)
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lemma real_root_pos_mult_exp:
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  "\<lbrakk>0 < m; 0 < n; 0 < x\<rbrakk> \<Longrightarrow> root (m * n) x = root m (root n x)"
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by (rule real_root_pos_unique, simp_all add: power_mult)
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lemma real_root_mult_exp:
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  "\<lbrakk>0 < m; 0 < n\<rbrakk> \<Longrightarrow> root (m * n) x = root m (root n x)"
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apply (rule linorder_cases [where x=x and y=0])
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apply (subgoal_tac "root (m * n) (- x) = root m (root n (- x))")
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apply (simp add: real_root_minus)
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apply (simp_all add: real_root_pos_mult_exp)
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done
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lemma real_root_commute:
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  "\<lbrakk>0 < m; 0 < n\<rbrakk> \<Longrightarrow> root m (root n x) = root n (root m x)"
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by (simp add: real_root_mult_exp [symmetric] mult_commute)
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text {* Monotonicity in first argument *}
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lemma real_root_strict_decreasing:
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  "\<lbrakk>0 < n; n < N; 1 < x\<rbrakk> \<Longrightarrow> root N x < root n x"
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apply (subgoal_tac "root n (root N x) ^ n < root N (root n x) ^ N", simp)
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apply (simp add: real_root_commute power_strict_increasing
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            del: real_root_pow_pos2)
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done
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lemma real_root_strict_increasing:
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  "\<lbrakk>0 < n; n < N; 0 < x; x < 1\<rbrakk> \<Longrightarrow> root n x < root N x"
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apply (subgoal_tac "root N (root n x) ^ N < root n (root N x) ^ n", simp)
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apply (simp add: real_root_commute power_strict_decreasing
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            del: real_root_pow_pos2)
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done
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lemma real_root_decreasing:
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  "\<lbrakk>0 < n; n < N; 1 \<le> x\<rbrakk> \<Longrightarrow> root N x \<le> root n x"
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by (auto simp add: order_le_less real_root_strict_decreasing)
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lemma real_root_increasing:
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  "\<lbrakk>0 < n; n < N; 0 \<le> x; x \<le> 1\<rbrakk> \<Longrightarrow> root n x \<le> root N x"
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by (auto simp add: order_le_less real_root_strict_increasing)
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text {* Roots of multiplication and division *}
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lemma real_root_mult_lemma:
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  "\<lbrakk>0 < n; 0 \<le> x; 0 \<le> y\<rbrakk> \<Longrightarrow> root n (x * y) = root n x * root n y"
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by (simp add: real_root_pos_unique mult_nonneg_nonneg power_mult_distrib)
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lemma real_root_inverse_lemma:
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  "\<lbrakk>0 < n; 0 \<le> x\<rbrakk> \<Longrightarrow> root n (inverse x) = inverse (root n x)"
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by (simp add: real_root_pos_unique power_inverse [symmetric])
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lemma real_root_mult:
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  assumes n: "0 < n"
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  shows "root n (x * y) = root n x * root n y"
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proof (rule linorder_le_cases, rule_tac [!] linorder_le_cases)
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  assume "0 \<le> x" and "0 \<le> y"
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  thus ?thesis by (rule real_root_mult_lemma [OF n])
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next
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  assume "0 \<le> x" and "y \<le> 0"
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  hence "0 \<le> x" and "0 \<le> - y" by simp_all
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  hence "root n (x * - y) = root n x * root n (- y)"
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    by (rule real_root_mult_lemma [OF n])
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  thus ?thesis by (simp add: real_root_minus [OF n])
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next
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  assume "x \<le> 0" and "0 \<le> y"
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  hence "0 \<le> - x" and "0 \<le> y" by simp_all
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  hence "root n (- x * y) = root n (- x) * root n y"
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    by (rule real_root_mult_lemma [OF n])
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  thus ?thesis by (simp add: real_root_minus [OF n])
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next
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  assume "x \<le> 0" and "y \<le> 0"
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  hence "0 \<le> - x" and "0 \<le> - y" by simp_all
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  hence "root n (- x * - y) = root n (- x) * root n (- y)"
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    by (rule real_root_mult_lemma [OF n])
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  thus ?thesis by (simp add: real_root_minus [OF n])
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qed
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lemma real_root_inverse:
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  assumes n: "0 < n"
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  shows "root n (inverse x) = inverse (root n x)"
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proof (rule linorder_le_cases)
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  assume "0 \<le> x"
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  thus ?thesis by (rule real_root_inverse_lemma [OF n])
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next
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  assume "x \<le> 0"
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  hence "0 \<le> - x" by simp
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  hence "root n (inverse (- x)) = inverse (root n (- x))"
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    by (rule real_root_inverse_lemma [OF n])
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  thus ?thesis by (simp add: real_root_minus [OF n])
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qed
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lemma real_root_divide:
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  "0 < n \<Longrightarrow> root n (x / y) = root n x / root n y"
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by (simp add: divide_inverse real_root_mult real_root_inverse)
huffman@22956
   292
huffman@22956
   293
lemma real_root_power:
huffman@22956
   294
  "0 < n \<Longrightarrow> root n (x ^ k) = root n x ^ k"
huffman@22956
   295
by (induct k, simp_all add: real_root_mult)
huffman@22721
   296
huffman@23042
   297
lemma real_root_abs: "0 < n \<Longrightarrow> root n \<bar>x\<bar> = \<bar>root n x\<bar>"
huffman@23042
   298
by (simp add: abs_if real_root_minus)
huffman@23042
   299
huffman@23042
   300
text {* Continuity and derivatives *}
huffman@23042
   301
huffman@23042
   302
lemma isCont_root_pos:
huffman@23042
   303
  assumes n: "0 < n"
huffman@23042
   304
  assumes x: "0 < x"
huffman@23042
   305
  shows "isCont (root n) x"
huffman@23042
   306
proof -
huffman@23042
   307
  have "isCont (root n) (root n x ^ n)"
huffman@23042
   308
  proof (rule isCont_inverse_function [where f="\<lambda>a. a ^ n"])
huffman@23042
   309
    show "0 < root n x" using n x by simp
huffman@23042
   310
    show "\<forall>z. \<bar>z - root n x\<bar> \<le> root n x \<longrightarrow> root n (z ^ n) = z"
huffman@23042
   311
      by (simp add: abs_le_iff real_root_power_cancel n)
huffman@23042
   312
    show "\<forall>z. \<bar>z - root n x\<bar> \<le> root n x \<longrightarrow> isCont (\<lambda>a. a ^ n) z"
huffman@23069
   313
      by (simp add: isCont_power)
huffman@23042
   314
  qed
huffman@23042
   315
  thus ?thesis using n x by simp
huffman@23042
   316
qed
huffman@23042
   317
huffman@23042
   318
lemma isCont_root_neg:
huffman@23042
   319
  "\<lbrakk>0 < n; x < 0\<rbrakk> \<Longrightarrow> isCont (root n) x"
huffman@23042
   320
apply (subgoal_tac "isCont (\<lambda>x. - root n (- x)) x")
huffman@23042
   321
apply (simp add: real_root_minus)
huffman@23069
   322
apply (rule isCont_o2 [OF isCont_minus [OF isCont_ident]])
huffman@23042
   323
apply (simp add: isCont_minus isCont_root_pos)
huffman@23042
   324
done
huffman@23042
   325
huffman@23042
   326
lemma isCont_root_zero:
huffman@23042
   327
  "0 < n \<Longrightarrow> isCont (root n) 0"
huffman@23042
   328
unfolding isCont_def
huffman@23042
   329
apply (rule LIM_I)
huffman@23042
   330
apply (rule_tac x="r ^ n" in exI, safe)
nipkow@25875
   331
apply (simp)
huffman@23042
   332
apply (simp add: real_root_abs [symmetric])
huffman@23042
   333
apply (rule_tac n="n" in power_less_imp_less_base, simp_all)
huffman@23042
   334
done
huffman@23042
   335
huffman@23042
   336
lemma isCont_real_root: "0 < n \<Longrightarrow> isCont (root n) x"
huffman@23042
   337
apply (rule_tac x=x and y=0 in linorder_cases)
huffman@23042
   338
apply (simp_all add: isCont_root_pos isCont_root_neg isCont_root_zero)
huffman@23042
   339
done
huffman@23042
   340
huffman@23042
   341
lemma DERIV_real_root:
huffman@23042
   342
  assumes n: "0 < n"
huffman@23042
   343
  assumes x: "0 < x"
huffman@23042
   344
  shows "DERIV (root n) x :> inverse (real n * root n x ^ (n - Suc 0))"
huffman@23042
   345
proof (rule DERIV_inverse_function)
huffman@23044
   346
  show "0 < x" using x .
huffman@23044
   347
  show "x < x + 1" by simp
huffman@23044
   348
  show "\<forall>y. 0 < y \<and> y < x + 1 \<longrightarrow> root n y ^ n = y"
huffman@23042
   349
    using n by simp
huffman@23042
   350
  show "DERIV (\<lambda>x. x ^ n) (root n x) :> real n * root n x ^ (n - Suc 0)"
huffman@23042
   351
    by (rule DERIV_pow)
huffman@23042
   352
  show "real n * root n x ^ (n - Suc 0) \<noteq> 0"
huffman@23042
   353
    using n x by simp
huffman@23042
   354
  show "isCont (root n) x"
huffman@23441
   355
    using n by (rule isCont_real_root)
huffman@23042
   356
qed
huffman@23042
   357
huffman@23046
   358
lemma DERIV_odd_real_root:
huffman@23046
   359
  assumes n: "odd n"
huffman@23046
   360
  assumes x: "x \<noteq> 0"
huffman@23046
   361
  shows "DERIV (root n) x :> inverse (real n * root n x ^ (n - Suc 0))"
huffman@23046
   362
proof (rule DERIV_inverse_function)
huffman@23046
   363
  show "x - 1 < x" by simp
huffman@23046
   364
  show "x < x + 1" by simp
huffman@23046
   365
  show "\<forall>y. x - 1 < y \<and> y < x + 1 \<longrightarrow> root n y ^ n = y"
huffman@23046
   366
    using n by (simp add: odd_real_root_pow)
huffman@23046
   367
  show "DERIV (\<lambda>x. x ^ n) (root n x) :> real n * root n x ^ (n - Suc 0)"
huffman@23046
   368
    by (rule DERIV_pow)
huffman@23046
   369
  show "real n * root n x ^ (n - Suc 0) \<noteq> 0"
huffman@23046
   370
    using odd_pos [OF n] x by simp
huffman@23046
   371
  show "isCont (root n) x"
huffman@23046
   372
    using odd_pos [OF n] by (rule isCont_real_root)
huffman@23046
   373
qed
huffman@23046
   374
huffman@22956
   375
subsection {* Square Root *}
huffman@20687
   376
huffman@22956
   377
definition
huffman@22956
   378
  sqrt :: "real \<Rightarrow> real" where
huffman@22956
   379
  "sqrt = root 2"
huffman@20687
   380
huffman@22956
   381
lemma pos2: "0 < (2::nat)" by simp
huffman@22956
   382
huffman@22956
   383
lemma real_sqrt_unique: "\<lbrakk>y\<twosuperior> = x; 0 \<le> y\<rbrakk> \<Longrightarrow> sqrt x = y"
huffman@22956
   384
unfolding sqrt_def by (rule real_root_pos_unique [OF pos2])
huffman@20687
   385
huffman@22956
   386
lemma real_sqrt_abs [simp]: "sqrt (x\<twosuperior>) = \<bar>x\<bar>"
huffman@22956
   387
apply (rule real_sqrt_unique)
huffman@22956
   388
apply (rule power2_abs)
huffman@22956
   389
apply (rule abs_ge_zero)
huffman@22956
   390
done
huffman@20687
   391
huffman@22956
   392
lemma real_sqrt_pow2 [simp]: "0 \<le> x \<Longrightarrow> (sqrt x)\<twosuperior> = x"
huffman@22956
   393
unfolding sqrt_def by (rule real_root_pow_pos2 [OF pos2])
huffman@22856
   394
huffman@22956
   395
lemma real_sqrt_pow2_iff [simp]: "((sqrt x)\<twosuperior> = x) = (0 \<le> x)"
huffman@22856
   396
apply (rule iffI)
huffman@22856
   397
apply (erule subst)
huffman@22856
   398
apply (rule zero_le_power2)
huffman@22856
   399
apply (erule real_sqrt_pow2)
huffman@20687
   400
done
huffman@20687
   401
huffman@22956
   402
lemma real_sqrt_zero [simp]: "sqrt 0 = 0"
huffman@22956
   403
unfolding sqrt_def by (rule real_root_zero)
huffman@22956
   404
huffman@22956
   405
lemma real_sqrt_one [simp]: "sqrt 1 = 1"
huffman@22956
   406
unfolding sqrt_def by (rule real_root_one [OF pos2])
huffman@22956
   407
huffman@22956
   408
lemma real_sqrt_minus: "sqrt (- x) = - sqrt x"
huffman@22956
   409
unfolding sqrt_def by (rule real_root_minus [OF pos2])
huffman@22956
   410
huffman@22956
   411
lemma real_sqrt_mult: "sqrt (x * y) = sqrt x * sqrt y"
huffman@22956
   412
unfolding sqrt_def by (rule real_root_mult [OF pos2])
huffman@22956
   413
huffman@22956
   414
lemma real_sqrt_inverse: "sqrt (inverse x) = inverse (sqrt x)"
huffman@22956
   415
unfolding sqrt_def by (rule real_root_inverse [OF pos2])
huffman@22956
   416
huffman@22956
   417
lemma real_sqrt_divide: "sqrt (x / y) = sqrt x / sqrt y"
huffman@22956
   418
unfolding sqrt_def by (rule real_root_divide [OF pos2])
huffman@22956
   419
huffman@22956
   420
lemma real_sqrt_power: "sqrt (x ^ k) = sqrt x ^ k"
huffman@22956
   421
unfolding sqrt_def by (rule real_root_power [OF pos2])
huffman@22956
   422
huffman@22956
   423
lemma real_sqrt_gt_zero: "0 < x \<Longrightarrow> 0 < sqrt x"
huffman@22956
   424
unfolding sqrt_def by (rule real_root_gt_zero [OF pos2])
huffman@22956
   425
huffman@22956
   426
lemma real_sqrt_ge_zero: "0 \<le> x \<Longrightarrow> 0 \<le> sqrt x"
huffman@22956
   427
unfolding sqrt_def by (rule real_root_ge_zero [OF pos2])
huffman@20687
   428
huffman@22956
   429
lemma real_sqrt_less_mono: "x < y \<Longrightarrow> sqrt x < sqrt y"
huffman@22956
   430
unfolding sqrt_def by (rule real_root_less_mono [OF pos2])
huffman@22956
   431
huffman@22956
   432
lemma real_sqrt_le_mono: "x \<le> y \<Longrightarrow> sqrt x \<le> sqrt y"
huffman@22956
   433
unfolding sqrt_def by (rule real_root_le_mono [OF pos2])
huffman@22956
   434
huffman@22956
   435
lemma real_sqrt_less_iff [simp]: "(sqrt x < sqrt y) = (x < y)"
huffman@22956
   436
unfolding sqrt_def by (rule real_root_less_iff [OF pos2])
huffman@22956
   437
huffman@22956
   438
lemma real_sqrt_le_iff [simp]: "(sqrt x \<le> sqrt y) = (x \<le> y)"
huffman@22956
   439
unfolding sqrt_def by (rule real_root_le_iff [OF pos2])
huffman@22956
   440
huffman@22956
   441
lemma real_sqrt_eq_iff [simp]: "(sqrt x = sqrt y) = (x = y)"
huffman@22956
   442
unfolding sqrt_def by (rule real_root_eq_iff [OF pos2])
huffman@22956
   443
huffman@22956
   444
lemmas real_sqrt_gt_0_iff [simp] = real_sqrt_less_iff [where x=0, simplified]
huffman@22956
   445
lemmas real_sqrt_lt_0_iff [simp] = real_sqrt_less_iff [where y=0, simplified]
huffman@22956
   446
lemmas real_sqrt_ge_0_iff [simp] = real_sqrt_le_iff [where x=0, simplified]
huffman@22956
   447
lemmas real_sqrt_le_0_iff [simp] = real_sqrt_le_iff [where y=0, simplified]
huffman@22956
   448
lemmas real_sqrt_eq_0_iff [simp] = real_sqrt_eq_iff [where y=0, simplified]
huffman@22956
   449
huffman@22956
   450
lemmas real_sqrt_gt_1_iff [simp] = real_sqrt_less_iff [where x=1, simplified]
huffman@22956
   451
lemmas real_sqrt_lt_1_iff [simp] = real_sqrt_less_iff [where y=1, simplified]
huffman@22956
   452
lemmas real_sqrt_ge_1_iff [simp] = real_sqrt_le_iff [where x=1, simplified]
huffman@22956
   453
lemmas real_sqrt_le_1_iff [simp] = real_sqrt_le_iff [where y=1, simplified]
huffman@22956
   454
lemmas real_sqrt_eq_1_iff [simp] = real_sqrt_eq_iff [where y=1, simplified]
huffman@20687
   455
huffman@23042
   456
lemma isCont_real_sqrt: "isCont sqrt x"
huffman@23042
   457
unfolding sqrt_def by (rule isCont_real_root [OF pos2])
huffman@23042
   458
huffman@23042
   459
lemma DERIV_real_sqrt:
huffman@23042
   460
  "0 < x \<Longrightarrow> DERIV sqrt x :> inverse (sqrt x) / 2"
huffman@23042
   461
unfolding sqrt_def by (rule DERIV_real_root [OF pos2, simplified])
huffman@23042
   462
huffman@20687
   463
lemma not_real_square_gt_zero [simp]: "(~ (0::real) < x*x) = (x = 0)"
huffman@20687
   464
apply auto
huffman@20687
   465
apply (cut_tac x = x and y = 0 in linorder_less_linear)
huffman@20687
   466
apply (simp add: zero_less_mult_iff)
huffman@20687
   467
done
huffman@20687
   468
huffman@20687
   469
lemma real_sqrt_abs2 [simp]: "sqrt(x*x) = \<bar>x\<bar>"
huffman@22856
   470
apply (subst power2_eq_square [symmetric])
huffman@20687
   471
apply (rule real_sqrt_abs)
huffman@20687
   472
done
huffman@20687
   473
huffman@20687
   474
lemma real_sqrt_pow2_gt_zero: "0 < x ==> 0 < (sqrt x)\<twosuperior>"
huffman@22956
   475
by simp (* TODO: delete *)
huffman@20687
   476
huffman@20687
   477
lemma real_sqrt_not_eq_zero: "0 < x ==> sqrt x \<noteq> 0"
huffman@22956
   478
by simp (* TODO: delete *)
huffman@20687
   479
huffman@20687
   480
lemma real_inv_sqrt_pow2: "0 < x ==> inverse (sqrt(x)) ^ 2 = inverse x"
huffman@22856
   481
by (simp add: power_inverse [symmetric])
huffman@20687
   482
huffman@20687
   483
lemma real_sqrt_eq_zero_cancel: "[| 0 \<le> x; sqrt(x) = 0|] ==> x = 0"
huffman@22956
   484
by simp
huffman@20687
   485
huffman@20687
   486
lemma real_sqrt_ge_one: "1 \<le> x ==> 1 \<le> sqrt x"
huffman@22956
   487
by simp
huffman@20687
   488
huffman@23049
   489
lemma real_sqrt_two_gt_zero [simp]: "0 < sqrt 2"
huffman@23049
   490
by simp
huffman@23049
   491
huffman@23049
   492
lemma real_sqrt_two_ge_zero [simp]: "0 \<le> sqrt 2"
huffman@23049
   493
by simp
huffman@23049
   494
huffman@23049
   495
lemma real_sqrt_two_gt_one [simp]: "1 < sqrt 2"
huffman@23049
   496
by simp
huffman@23049
   497
huffman@22443
   498
lemma sqrt_divide_self_eq:
huffman@22443
   499
  assumes nneg: "0 \<le> x"
huffman@22443
   500
  shows "sqrt x / x = inverse (sqrt x)"
huffman@22443
   501
proof cases
huffman@22443
   502
  assume "x=0" thus ?thesis by simp
huffman@22443
   503
next
huffman@22443
   504
  assume nz: "x\<noteq>0" 
huffman@22443
   505
  hence pos: "0<x" using nneg by arith
huffman@22443
   506
  show ?thesis
huffman@22443
   507
  proof (rule right_inverse_eq [THEN iffD1, THEN sym]) 
huffman@22443
   508
    show "sqrt x / x \<noteq> 0" by (simp add: divide_inverse nneg nz) 
huffman@22443
   509
    show "inverse (sqrt x) / (sqrt x / x) = 1"
huffman@22443
   510
      by (simp add: divide_inverse mult_assoc [symmetric] 
huffman@22443
   511
                  power2_eq_square [symmetric] real_inv_sqrt_pow2 pos nz) 
huffman@22443
   512
  qed
huffman@22443
   513
qed
huffman@22443
   514
huffman@22721
   515
lemma real_divide_square_eq [simp]: "(((r::real) * a) / (r * r)) = a / r"
huffman@22721
   516
apply (simp add: divide_inverse)
huffman@22721
   517
apply (case_tac "r=0")
huffman@22721
   518
apply (auto simp add: mult_ac)
huffman@22721
   519
done
huffman@22721
   520
huffman@23049
   521
lemma lemma_real_divide_sqrt_less: "0 < u ==> u / sqrt 2 < u"
huffman@23049
   522
by (simp add: divide_less_eq mult_compare_simps)
huffman@23049
   523
huffman@23049
   524
lemma four_x_squared: 
huffman@23049
   525
  fixes x::real
huffman@23049
   526
  shows "4 * x\<twosuperior> = (2 * x)\<twosuperior>"
huffman@23049
   527
by (simp add: power2_eq_square)
huffman@23049
   528
huffman@22856
   529
subsection {* Square Root of Sum of Squares *}
huffman@22856
   530
huffman@22856
   531
lemma real_sqrt_mult_self_sum_ge_zero [simp]: "0 \<le> sqrt(x*x + y*y)"
huffman@22968
   532
by (rule real_sqrt_ge_zero [OF sum_squares_ge_zero])
huffman@22856
   533
huffman@22856
   534
lemma real_sqrt_sum_squares_ge_zero [simp]: "0 \<le> sqrt (x\<twosuperior> + y\<twosuperior>)"
huffman@22961
   535
by simp
huffman@22856
   536
huffman@23049
   537
declare real_sqrt_sum_squares_ge_zero [THEN abs_of_nonneg, simp]
huffman@23049
   538
huffman@22856
   539
lemma real_sqrt_sum_squares_mult_ge_zero [simp]:
huffman@22856
   540
     "0 \<le> sqrt ((x\<twosuperior> + y\<twosuperior>)*(xa\<twosuperior> + ya\<twosuperior>))"
huffman@22856
   541
by (auto intro!: real_sqrt_ge_zero simp add: zero_le_mult_iff)
huffman@22856
   542
huffman@22856
   543
lemma real_sqrt_sum_squares_mult_squared_eq [simp]:
huffman@22856
   544
     "sqrt ((x\<twosuperior> + y\<twosuperior>) * (xa\<twosuperior> + ya\<twosuperior>)) ^ 2 = (x\<twosuperior> + y\<twosuperior>) * (xa\<twosuperior> + ya\<twosuperior>)"
huffman@22956
   545
by (auto simp add: zero_le_mult_iff)
huffman@22856
   546
huffman@23049
   547
lemma real_sqrt_sum_squares_eq_cancel: "sqrt (x\<twosuperior> + y\<twosuperior>) = x \<Longrightarrow> y = 0"
huffman@23049
   548
by (drule_tac f = "%x. x\<twosuperior>" in arg_cong, simp)
huffman@23049
   549
huffman@23049
   550
lemma real_sqrt_sum_squares_eq_cancel2: "sqrt (x\<twosuperior> + y\<twosuperior>) = y \<Longrightarrow> x = 0"
huffman@23049
   551
by (drule_tac f = "%x. x\<twosuperior>" in arg_cong, simp)
huffman@23049
   552
huffman@23049
   553
lemma real_sqrt_sum_squares_ge1 [simp]: "x \<le> sqrt (x\<twosuperior> + y\<twosuperior>)"
huffman@22856
   554
by (rule power2_le_imp_le, simp_all)
huffman@22856
   555
huffman@23049
   556
lemma real_sqrt_sum_squares_ge2 [simp]: "y \<le> sqrt (x\<twosuperior> + y\<twosuperior>)"
huffman@23049
   557
by (rule power2_le_imp_le, simp_all)
huffman@23049
   558
huffman@23049
   559
lemma real_sqrt_ge_abs1 [simp]: "\<bar>x\<bar> \<le> sqrt (x\<twosuperior> + y\<twosuperior>)"
huffman@22856
   560
by (rule power2_le_imp_le, simp_all)
huffman@22856
   561
huffman@23049
   562
lemma real_sqrt_ge_abs2 [simp]: "\<bar>y\<bar> \<le> sqrt (x\<twosuperior> + y\<twosuperior>)"
huffman@23049
   563
by (rule power2_le_imp_le, simp_all)
huffman@23049
   564
huffman@23049
   565
lemma le_real_sqrt_sumsq [simp]: "x \<le> sqrt (x * x + y * y)"
huffman@23049
   566
by (simp add: power2_eq_square [symmetric])
huffman@23049
   567
huffman@22858
   568
lemma power2_sum:
huffman@22858
   569
  fixes x y :: "'a::{number_ring,recpower}"
huffman@22858
   570
  shows "(x + y)\<twosuperior> = x\<twosuperior> + y\<twosuperior> + 2 * x * y"
nipkow@23477
   571
by (simp add: ring_distribs power2_eq_square)
huffman@22858
   572
huffman@22858
   573
lemma power2_diff:
huffman@22858
   574
  fixes x y :: "'a::{number_ring,recpower}"
huffman@22858
   575
  shows "(x - y)\<twosuperior> = x\<twosuperior> + y\<twosuperior> - 2 * x * y"
nipkow@23477
   576
by (simp add: ring_distribs power2_eq_square)
huffman@22858
   577
huffman@22858
   578
lemma real_sqrt_sum_squares_triangle_ineq:
huffman@22858
   579
  "sqrt ((a + c)\<twosuperior> + (b + d)\<twosuperior>) \<le> sqrt (a\<twosuperior> + b\<twosuperior>) + sqrt (c\<twosuperior> + d\<twosuperior>)"
huffman@22858
   580
apply (rule power2_le_imp_le, simp)
huffman@22858
   581
apply (simp add: power2_sum)
huffman@22858
   582
apply (simp only: mult_assoc right_distrib [symmetric])
huffman@22858
   583
apply (rule mult_left_mono)
huffman@22858
   584
apply (rule power2_le_imp_le)
huffman@22858
   585
apply (simp add: power2_sum power_mult_distrib)
nipkow@23477
   586
apply (simp add: ring_distribs)
huffman@22858
   587
apply (subgoal_tac "0 \<le> b\<twosuperior> * c\<twosuperior> + a\<twosuperior> * d\<twosuperior> - 2 * (a * c) * (b * d)", simp)
huffman@22858
   588
apply (rule_tac b="(a * d - b * c)\<twosuperior>" in ord_le_eq_trans)
huffman@22858
   589
apply (rule zero_le_power2)
huffman@22858
   590
apply (simp add: power2_diff power_mult_distrib)
huffman@22858
   591
apply (simp add: mult_nonneg_nonneg)
huffman@22858
   592
apply simp
huffman@22858
   593
apply (simp add: add_increasing)
huffman@22858
   594
done
huffman@22858
   595
huffman@23122
   596
lemma real_sqrt_sum_squares_less:
huffman@23122
   597
  "\<lbrakk>\<bar>x\<bar> < u / sqrt 2; \<bar>y\<bar> < u / sqrt 2\<rbrakk> \<Longrightarrow> sqrt (x\<twosuperior> + y\<twosuperior>) < u"
huffman@23122
   598
apply (rule power2_less_imp_less, simp)
huffman@23122
   599
apply (drule power_strict_mono [OF _ abs_ge_zero pos2])
huffman@23122
   600
apply (drule power_strict_mono [OF _ abs_ge_zero pos2])
huffman@23122
   601
apply (simp add: power_divide)
huffman@23122
   602
apply (drule order_le_less_trans [OF abs_ge_zero])
huffman@23122
   603
apply (simp add: zero_less_divide_iff)
huffman@23122
   604
done
huffman@23122
   605
huffman@23049
   606
text{*Needed for the infinitely close relation over the nonstandard
huffman@23049
   607
    complex numbers*}
huffman@23049
   608
lemma lemma_sqrt_hcomplex_capprox:
huffman@23049
   609
     "[| 0 < u; x < u/2; y < u/2; 0 \<le> x; 0 \<le> y |] ==> sqrt (x\<twosuperior> + y\<twosuperior>) < u"
huffman@23049
   610
apply (rule_tac y = "u/sqrt 2" in order_le_less_trans)
huffman@23049
   611
apply (erule_tac [2] lemma_real_divide_sqrt_less)
huffman@23049
   612
apply (rule power2_le_imp_le)
huffman@23049
   613
apply (auto simp add: real_0_le_divide_iff power_divide)
huffman@23049
   614
apply (rule_tac t = "u\<twosuperior>" in real_sum_of_halves [THEN subst])
huffman@23049
   615
apply (rule add_mono)
huffman@30273
   616
apply (auto simp add: four_x_squared intro: power_mono)
huffman@23049
   617
done
huffman@23049
   618
huffman@22956
   619
text "Legacy theorem names:"
huffman@22956
   620
lemmas real_root_pos2 = real_root_power_cancel
huffman@22956
   621
lemmas real_root_pos_pos = real_root_gt_zero [THEN order_less_imp_le]
huffman@22956
   622
lemmas real_root_pos_pos_le = real_root_ge_zero
huffman@22956
   623
lemmas real_sqrt_mult_distrib = real_sqrt_mult
huffman@22956
   624
lemmas real_sqrt_mult_distrib2 = real_sqrt_mult
huffman@22956
   625
lemmas real_sqrt_eq_zero_cancel_iff = real_sqrt_eq_0_iff
huffman@22956
   626
huffman@22956
   627
(* needed for CauchysMeanTheorem.het_base from AFP *)
huffman@22956
   628
lemma real_root_pos: "0 < x \<Longrightarrow> root (Suc n) (x ^ (Suc n)) = x"
huffman@22956
   629
by (rule real_root_power_cancel [OF zero_less_Suc order_less_imp_le])
huffman@22956
   630
paulson@14324
   631
end