1.1 --- a/src/Pure/raw_simplifier.ML	Sat Mar 30 17:13:21 2013 +0100
     1.2 +++ b/src/Pure/raw_simplifier.ML	Sat Mar 30 17:27:21 2013 +0100
     1.3 @@ -883,7 +883,10 @@
     1.4  
     1.5  fun uncond_skel ((_, weak), (lhs, rhs)) =
     1.6    if null weak then rhs  (*optimization*)
     1.7 -  else if exists_Const (fn (c, _) => member (op =) weak (true, c)) lhs then skel0
     1.8 +  else if exists_subterm
     1.9 +    (fn Const (a, _) => member (op =) weak (true, a)
    1.10 +      | Free (a, _) => member (op =) weak (false, a)
    1.11 +      | _ => false) lhs then skel0
    1.12    else rhs;
    1.13  
    1.14  (*Behaves like unconditional rule if rhs does not contain vars not in the lhs.