no need thanks to "Code.abort"

--- a/src/HOL/BNF/BNF_FP_Base.thy	Wed Sep 18 16:44:19 2013 +0200
+++ b/src/HOL/BNF/BNF_FP_Base.thy	Wed Sep 18 17:36:47 2013 +0200
@@ -13,11 +13,6 @@
 imports BNF_Comp BNF_Ctr_Sugar
 begin
 
-definition code_unspec :: "(unit \<Rightarrow> 'a) \<Rightarrow> 'a" where
-[code del]: "code_unspec f = f ()"
-
-code_abort code_unspec
-
 lemma mp_conj: "(P \<longrightarrow> Q) \<and> R \<Longrightarrow> P \<Longrightarrow> R \<and> Q"
 by auto