-- | computes the formulas for the relations between variables
congruence_ax_vars :: [SORT] -> [CASLTERM] -> [CASLTERM] -> [CASLFORMULA]
congruence_ax_vars (s : ss) (x : xs) (y : ys) = form : forms
     where
           form = mkPredication (freePredSymb s) [x, y]
           forms = congruence_ax_vars ss xs ys
congruence_ax_vars :: [SORT] -> [CASLTERM] -> [CASLTERM] -> [CASLFORMULA]
congruence_ax_vars (s : ss) (x : xs) (y : ys) = form : forms
     where
           form = mkPredication (freePredSymb s) [x, y]
           forms = congruence_ax_vars ss xs ys
congruence_ax_vars (s : ss) (x : xs) (y : ys) = form : forms
     where
           form = mkPredication (freePredSymb s) [x, y]
           forms = congruence_ax_vars ss xs ys