1.1 --- a/src/HOL/Log.thy Wed Apr 18 14:29:16 2012 +0200
1.2 +++ b/src/HOL/Log.thy Wed Apr 18 14:29:17 2012 +0200
1.3 @@ -199,12 +199,26 @@
1.4 apply (subst powr_add, simp, simp)
1.5 done
1.6
1.7 -lemma powr_realpow2: "0 <= x ==> 0 < n ==> x^n = (if (x = 0) then 0
1.8 - else x powr (real n))"
1.9 +lemma powr_realpow2: "0 <= x ==> 0 < n ==> x^n = (if (x = 0) then 0 else x powr (real n))"
1.10 apply (case_tac "x = 0", simp, simp)
1.11 apply (rule powr_realpow [THEN sym], simp)
1.12 done
1.13
1.14 +lemma powr_int:
1.15 + assumes "x > 0"
1.16 + shows "x powr i = (if i \<ge> 0 then x ^ nat i else 1 / x ^ nat (-i))"
1.17 +proof cases
1.18 + assume "i < 0"
1.19 + have r: "x powr i = 1 / x powr (-i)" by (simp add: powr_minus field_simps)
1.20 + show ?thesis using `i < 0` `x > 0` by (simp add: r field_simps powr_realpow[symmetric])
1.21 +qed (simp add: assms powr_realpow[symmetric])
1.22 +
1.23 +lemma powr_numeral: "0 < x \<Longrightarrow> x powr numeral n = x^numeral n"
1.24 + using powr_realpow[of x "numeral n"] by simp
1.25 +
1.26 +lemma powr_neg_numeral: "0 < x \<Longrightarrow> x powr neg_numeral n = 1 / x^numeral n"
1.27 + using powr_int[of x "neg_numeral n"] by simp
1.28 +
1.29 lemma root_powr_inverse:
1.30 "0 < n \<Longrightarrow> 0 < x \<Longrightarrow> root n x = x powr (1/n)"
1.31 by (auto simp: root_def powr_realpow[symmetric] powr_powr)