Had to rename params because variable names in an induction rule changed.

--- a/src/HOL/IMP/Hoare.ML	Fri May 17 12:23:44 1996 +0200
+++ b/src/HOL/IMP/Hoare.ML	Fri May 17 12:24:47 1996 +0200
@@ -19,8 +19,10 @@
 by (rtac impI 1);
 by (etac induct2 1);
  br Gamma_mono 1;
+by(prune_params_tac);
+by(rename_tac "s t" 1);
 by (rewtac Gamma_def);  
-by(eres_inst_tac [("x","a")] allE 1);
+by(eres_inst_tac [("x","s")] allE 1);
 by (safe_tac comp_cs);
   by(ALLGOALS Asm_full_simp_tac);
 qed "hoare_sound";