--- a/src/HOL/Library/Quotient_Set.thy Wed Jun 17 10:57:11 2015 +0200
+++ b/src/HOL/Library/Quotient_Set.thy Wed Jun 17 11:03:05 2015 +0200
@@ -2,13 +2,13 @@
Author: Cezary Kaliszyk and Christian Urban
*)
-section {* Quotient infrastructure for the set type *}
+section \<open>Quotient infrastructure for the set type\<close>
theory Quotient_Set
imports Main Quotient_Syntax
begin
-subsection {* Contravariant set map (vimage) and set relator, rules for the Quotient package *}
+subsection \<open>Contravariant set map (vimage) and set relator, rules for the Quotient package\<close>
definition "rel_vset R xs ys \<equiv> \<forall>x y. R x y \<longrightarrow> x \<in> xs \<longleftrightarrow> y \<in> ys"