evaluation of THE with a non-singleton set raises a Match exception during the evaluation to yield a potential counterexample in quickcheck.

--- a/src/HOL/Enum.thy	Thu Jan 26 10:59:47 2012 +0100
+++ b/src/HOL/Enum.thy	Thu Jan 26 12:03:35 2012 +0100
@@ -777,6 +777,7 @@
 qed
 
 code_abort enum_the
+code_const enum_the (Eval "(fn p => raise Match)")
 
 subsection {* Further operations on finite types *}