extenv1 x t (TEnv env vs) = TEnv (E.extenv1 x t env) (vs `unionS` fromListS (tv t))
extenv1 x t (TEnv env vs) = TEnv (E.extenv1 x t env) (vs `unionS` fromListS (tv t))
extenv1 x t (TEnv env vs) = TEnv (E.extenv1 x t env) (vs `unionS` fromListS (tv t))