--- a/src/HOL/NthRoot.thy Thu Oct 23 14:04:05 2014 +0200
+++ b/src/HOL/NthRoot.thy Thu Oct 23 14:04:05 2014 +0200
@@ -7,7 +7,7 @@
header {* Nth Roots of Real Numbers *}
theory NthRoot
-imports Parity Deriv
+imports Deriv
begin
lemma abs_sgn_eq: "abs (sgn x :: real) = (if x = 0 then 0 else 1)"