extendTvSubstList :: TvSubst -> [TyVar] -> [Type] -> TvSubst
extendTvSubstList (TvSubst in_scope tenv) tvs tys
  = TvSubst in_scope (extendVarEnvList tenv (tvs `zip` tys))
extendTvSubstList :: TvSubst -> [TyVar] -> [Type] -> TvSubst
extendTvSubstList (TvSubst in_scope tenv) tvs tys
  = TvSubst in_scope (extendVarEnvList tenv (tvs `zip` tys))
extendTvSubstList (TvSubst in_scope tenv) tvs tys
  = TvSubst in_scope (extendVarEnvList tenv (tvs `zip` tys))