clarified context;

--- a/src/Pure/skip_proof.ML	Tue Jul 28 20:05:53 2015 +0200
+++ b/src/Pure/skip_proof.ML	Tue Jul 28 20:07:05 2015 +0200
@@ -38,6 +38,6 @@
 (* cheat_tac *)
 
 fun cheat_tac ctxt i st =
-  resolve_tac ctxt [make_thm (Thm.theory_of_thm st) (Var (("A", 0), propT))] i st;
+  resolve_tac ctxt [make_thm (Proof_Context.theory_of ctxt) (Var (("A", 0), propT))] i st;
 
 end;