# HG changeset patch
# User wenzelm
# Date 1622890672 -7200
# Node ID f143d0a4cb6af7781036a3220a863f6f3b300e07
# Parent  1c5dcba6925f129500a062c41acbcf523818c44d
clarified examples;

diff -r 1c5dcba6925f -r f143d0a4cb6a src/HOL/Examples/Sqrt.thy
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Examples/Sqrt.thy	Sat Jun 05 12:57:52 2021 +0200
@@ -0,0 +1,104 @@
+(*  Title:      HOL/Examples/Sqrt.thy
+    Author:     Makarius
+    Author:     Tobias Nipkow, TU Muenchen
+*)
+
+section \<open>Square roots of primes are irrational\<close>
+
+theory Sqrt
+  imports Complex_Main "HOL-Computational_Algebra.Primes"
+begin
+
+text \<open>
+  The square root of any prime number (including 2) is irrational.
+\<close>
+
+theorem sqrt_prime_irrational:
+  fixes p :: nat
+  assumes "prime p"
+  shows "sqrt p \<notin> \<rat>"
+proof
+  from \<open>prime p\<close> have p: "p > 1" by (rule prime_gt_1_nat)
+  assume "sqrt p \<in> \<rat>"
+  then obtain m n :: nat
+    where n: "n \<noteq> 0"
+      and sqrt_rat: "\<bar>sqrt p\<bar> = m / n"
+      and "coprime m n" by (rule Rats_abs_nat_div_natE)
+  have eq: "m\<^sup>2 = p * n\<^sup>2"
+  proof -
+    from n and sqrt_rat have "m = \<bar>sqrt p\<bar> * n" by simp
+    then have "m\<^sup>2 = (sqrt p)\<^sup>2 * n\<^sup>2" by (simp add: power_mult_distrib)
+    also have "(sqrt p)\<^sup>2 = p" by simp
+    also have "\<dots> * n\<^sup>2 = p * n\<^sup>2" by simp
+    finally show ?thesis by linarith
+  qed
+  have "p dvd m \<and> p dvd n"
+  proof
+    from eq have "p dvd m\<^sup>2" ..
+    with \<open>prime p\<close> show "p dvd m" by (rule prime_dvd_power)
+    then obtain k where "m = p * k" ..
+    with eq have "p * n\<^sup>2 = p\<^sup>2 * k\<^sup>2" by algebra
+    with p have "n\<^sup>2 = p * k\<^sup>2" by (simp add: power2_eq_square)
+    then have "p dvd n\<^sup>2" ..
+    with \<open>prime p\<close> show "p dvd n" by (rule prime_dvd_power)
+  qed
+  then have "p dvd gcd m n" by simp
+  with \<open>coprime m n\<close> have "p = 1" by simp
+  with p show False by simp
+qed
+
+corollary sqrt_2_not_rat: "sqrt 2 \<notin> \<rat>"
+  using sqrt_prime_irrational [of 2] by simp
+
+text \<open>
+  Here is an alternative version of the main proof, using mostly linear
+  forward-reasoning. While this results in less top-down structure, it is
+  probably closer to proofs seen in mathematics.
+\<close>
+
+theorem
+  fixes p :: nat
+  assumes "prime p"
+  shows "sqrt p \<notin> \<rat>"
+proof
+  from \<open>prime p\<close> have p: "p > 1" by (rule prime_gt_1_nat)
+  assume "sqrt p \<in> \<rat>"
+  then obtain m n :: nat
+    where n: "n \<noteq> 0"
+      and sqrt_rat: "\<bar>sqrt p\<bar> = m / n"
+      and "coprime m n" by (rule Rats_abs_nat_div_natE)
+  from n and sqrt_rat have "m = \<bar>sqrt p\<bar> * n" by simp
+  then have "m\<^sup>2 = (sqrt p)\<^sup>2 * n\<^sup>2" by (auto simp add: power2_eq_square)
+  also have "(sqrt p)\<^sup>2 = p" by simp
+  also have "\<dots> * n\<^sup>2 = p * n\<^sup>2" by simp
+  finally have eq: "m\<^sup>2 = p * n\<^sup>2" by linarith
+  then have "p dvd m\<^sup>2" ..
+  with \<open>prime p\<close> have dvd_m: "p dvd m" by (rule prime_dvd_power)
+  then obtain k where "m = p * k" ..
+  with eq have "p * n\<^sup>2 = p\<^sup>2 * k\<^sup>2" by algebra
+  with p have "n\<^sup>2 = p * k\<^sup>2" by (simp add: power2_eq_square)
+  then have "p dvd n\<^sup>2" ..
+  with \<open>prime p\<close> have "p dvd n" by (rule prime_dvd_power)
+  with dvd_m have "p dvd gcd m n" by (rule gcd_greatest)
+  with \<open>coprime m n\<close> have "p = 1" by simp
+  with p show False by simp
+qed
+
+
+text \<open>
+  Another old chestnut, which is a consequence of the irrationality of
+  \<^term>\<open>sqrt 2\<close>.
+\<close>
+
+lemma "\<exists>a b::real. a \<notin> \<rat> \<and> b \<notin> \<rat> \<and> a powr b \<in> \<rat>" (is "\<exists>a b. ?P a b")
+proof (cases "sqrt 2 powr sqrt 2 \<in> \<rat>")
+  case True
+  with sqrt_2_not_rat have "?P (sqrt 2) (sqrt 2)" by simp
+  then show ?thesis by blast
+next
+  case False
+  with sqrt_2_not_rat powr_powr have "?P (sqrt 2 powr sqrt 2) (sqrt 2)" by simp
+  then show ?thesis by blast
+qed
+
+end
diff -r 1c5dcba6925f -r f143d0a4cb6a src/HOL/ROOT
--- a/src/HOL/ROOT	Sat Jun 05 12:45:00 2021 +0200
+++ b/src/HOL/ROOT	Sat Jun 05 12:57:52 2021 +0200
@@ -20,7 +20,7 @@
     Notable Examples in Isabelle/HOL.
   "
   sessions
-    "HOL-Library"
+    "HOL-Computational_Algebra"
   theories
     Adhoc_Overloading_Examples
     Ackermann
@@ -36,6 +36,7 @@
     Peirce
     Records
     Seq
+    Sqrt
   document_files
     "root.bib"
     "root.tex"
@@ -706,7 +707,6 @@
     Sketch_and_Explore
     Sorting_Algorithms_Examples
     Specifications_with_bundle_mixins
-    Sqrt
     Sqrt_Script
     Sudoku
     Sum_of_Powers
diff -r 1c5dcba6925f -r f143d0a4cb6a src/HOL/ex/Sqrt.thy
--- a/src/HOL/ex/Sqrt.thy	Sat Jun 05 12:45:00 2021 +0200
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,104 +0,0 @@
-(*  Title:      HOL/ex/Sqrt.thy
-    Author:     Makarius
-    Author:     Tobias Nipkow, TU Muenchen
-*)
-
-section \<open>Square roots of primes are irrational\<close>
-
-theory Sqrt
-  imports Complex_Main "HOL-Computational_Algebra.Primes"
-begin
-
-text \<open>
-  The square root of any prime number (including 2) is irrational.
-\<close>
-
-theorem sqrt_prime_irrational:
-  fixes p :: nat
-  assumes "prime p"
-  shows "sqrt p \<notin> \<rat>"
-proof
-  from \<open>prime p\<close> have p: "p > 1" by (rule prime_gt_1_nat)
-  assume "sqrt p \<in> \<rat>"
-  then obtain m n :: nat
-    where n: "n \<noteq> 0"
-      and sqrt_rat: "\<bar>sqrt p\<bar> = m / n"
-      and "coprime m n" by (rule Rats_abs_nat_div_natE)
-  have eq: "m\<^sup>2 = p * n\<^sup>2"
-  proof -
-    from n and sqrt_rat have "m = \<bar>sqrt p\<bar> * n" by simp
-    then have "m\<^sup>2 = (sqrt p)\<^sup>2 * n\<^sup>2" by (simp add: power_mult_distrib)
-    also have "(sqrt p)\<^sup>2 = p" by simp
-    also have "\<dots> * n\<^sup>2 = p * n\<^sup>2" by simp
-    finally show ?thesis by linarith
-  qed
-  have "p dvd m \<and> p dvd n"
-  proof
-    from eq have "p dvd m\<^sup>2" ..
-    with \<open>prime p\<close> show "p dvd m" by (rule prime_dvd_power)
-    then obtain k where "m = p * k" ..
-    with eq have "p * n\<^sup>2 = p\<^sup>2 * k\<^sup>2" by algebra
-    with p have "n\<^sup>2 = p * k\<^sup>2" by (simp add: power2_eq_square)
-    then have "p dvd n\<^sup>2" ..
-    with \<open>prime p\<close> show "p dvd n" by (rule prime_dvd_power)
-  qed
-  then have "p dvd gcd m n" by simp
-  with \<open>coprime m n\<close> have "p = 1" by simp
-  with p show False by simp
-qed
-
-corollary sqrt_2_not_rat: "sqrt 2 \<notin> \<rat>"
-  using sqrt_prime_irrational [of 2] by simp
-
-text \<open>
-  Here is an alternative version of the main proof, using mostly linear
-  forward-reasoning. While this results in less top-down structure, it is
-  probably closer to proofs seen in mathematics.
-\<close>
-
-theorem
-  fixes p :: nat
-  assumes "prime p"
-  shows "sqrt p \<notin> \<rat>"
-proof
-  from \<open>prime p\<close> have p: "p > 1" by (rule prime_gt_1_nat)
-  assume "sqrt p \<in> \<rat>"
-  then obtain m n :: nat
-    where n: "n \<noteq> 0"
-      and sqrt_rat: "\<bar>sqrt p\<bar> = m / n"
-      and "coprime m n" by (rule Rats_abs_nat_div_natE)
-  from n and sqrt_rat have "m = \<bar>sqrt p\<bar> * n" by simp
-  then have "m\<^sup>2 = (sqrt p)\<^sup>2 * n\<^sup>2" by (auto simp add: power2_eq_square)
-  also have "(sqrt p)\<^sup>2 = p" by simp
-  also have "\<dots> * n\<^sup>2 = p * n\<^sup>2" by simp
-  finally have eq: "m\<^sup>2 = p * n\<^sup>2" by linarith
-  then have "p dvd m\<^sup>2" ..
-  with \<open>prime p\<close> have dvd_m: "p dvd m" by (rule prime_dvd_power)
-  then obtain k where "m = p * k" ..
-  with eq have "p * n\<^sup>2 = p\<^sup>2 * k\<^sup>2" by algebra
-  with p have "n\<^sup>2 = p * k\<^sup>2" by (simp add: power2_eq_square)
-  then have "p dvd n\<^sup>2" ..
-  with \<open>prime p\<close> have "p dvd n" by (rule prime_dvd_power)
-  with dvd_m have "p dvd gcd m n" by (rule gcd_greatest)
-  with \<open>coprime m n\<close> have "p = 1" by simp
-  with p show False by simp
-qed
-
-
-text \<open>
-  Another old chestnut, which is a consequence of the irrationality of
-  \<^term>\<open>sqrt 2\<close>.
-\<close>
-
-lemma "\<exists>a b::real. a \<notin> \<rat> \<and> b \<notin> \<rat> \<and> a powr b \<in> \<rat>" (is "\<exists>a b. ?P a b")
-proof (cases "sqrt 2 powr sqrt 2 \<in> \<rat>")
-  case True
-  with sqrt_2_not_rat have "?P (sqrt 2) (sqrt 2)" by simp
-  then show ?thesis by blast
-next
-  case False
-  with sqrt_2_not_rat powr_powr have "?P (sqrt 2 powr sqrt 2) (sqrt 2)" by simp
-  then show ?thesis by blast
-qed
-
-end
diff -r 1c5dcba6925f -r f143d0a4cb6a src/HOL/ex/Sqrt_Script.thy
--- a/src/HOL/ex/Sqrt_Script.thy	Sat Jun 05 12:45:00 2021 +0200
+++ b/src/HOL/ex/Sqrt_Script.thy	Sat Jun 05 12:57:52 2021 +0200
@@ -5,14 +5,14 @@
 
 section \<open>Square roots of primes are irrational (script version)\<close>
 
-theory Sqrt_Script
-imports Complex_Main "HOL-Computational_Algebra.Primes"
-begin
+text \<open>
+  Contrast this linear Isabelle/Isar script with the more mathematical version
+  in \<^file>\<open>~~/src/HOL/Examples/Sqrt.thy\<close> by Makarius Wenzel.
+\<close>
 
-text \<open>
-  \medskip Contrast this linear Isabelle/Isar script with Markus
-  Wenzel's more mathematical version.
-\<close>
+theory Sqrt_Script
+  imports Complex_Main "HOL-Computational_Algebra.Primes"
+begin
 
 subsection \<open>Preliminaries\<close>