1.1 --- a/src/HOL/Divides.thy	Tue Mar 27 15:53:48 2012 +0200
     1.2 +++ b/src/HOL/Divides.thy	Tue Mar 27 16:04:51 2012 +0200
     1.3 @@ -283,6 +283,15 @@
     1.4      by (simp only: mod_mult_eq [symmetric])
     1.5  qed
     1.6  
     1.7 +text {* Exponentiation respects modular equivalence. *}
     1.8 +
     1.9 +lemma power_mod: "(a mod b)^n mod b = a^n mod b"
    1.10 +apply (induct n, simp_all)
    1.11 +apply (rule mod_mult_right_eq [THEN trans])
    1.12 +apply (simp (no_asm_simp))
    1.13 +apply (rule mod_mult_eq [symmetric])
    1.14 +done
    1.15 +
    1.16  lemma mod_mod_cancel:
    1.17    assumes "c dvd b"
    1.18    shows "a mod b mod c = a mod c"
    1.19 @@ -2179,13 +2188,6 @@
    1.20    using zmod_zdiv_equality[where a="m" and b="n"]
    1.21    by (simp add: algebra_simps) (* FIXME: generalize *)
    1.22  
    1.23 -lemma zpower_zmod: "((x::int) mod m)^y mod m = x^y mod m"
    1.24 -apply (induct "y", auto)
    1.25 -apply (rule mod_mult_right_eq [THEN trans])
    1.26 -apply (simp (no_asm_simp))
    1.27 -apply (rule mod_mult_eq [symmetric])
    1.28 -done (* FIXME: generalize *)
    1.29 -
    1.30  lemma zdiv_int: "int (a div b) = (int a) div (int b)"
    1.31  apply (subst split_div, auto)
    1.32  apply (subst split_zdiv, auto)
    1.33 @@ -2228,7 +2230,7 @@
    1.34    mod_add_right_eq [symmetric]
    1.35    mod_mult_right_eq[symmetric]
    1.36    mod_mult_left_eq [symmetric]
    1.37 -  zpower_zmod
    1.38 +  power_mod
    1.39    zminus_zmod zdiff_zmod_left zdiff_zmod_right
    1.40  
    1.41  text {* Distributive laws for function @{text nat}. *}