+ if R.are_convertible subst context t1' t2' then
+ true,subst,metasenv
+ else
+ (try
+ let subst,metasenv =
+ fo_unif_subst subst context metasenv t1' t2'
+ in
+ true,subst,metasenv
+ with
+ Not_found -> false,subst,metasenv)
+ ) (true,subst,metasenv) ln lm