homomorphy_form (Mixfix_formula t) = Mixfix_formula t'
     where t' = homomorphy_term t
homomorphy_form (Mixfix_formula t) = Mixfix_formula t'
     where t' = homomorphy_term t
homomorphy_form (Mixfix_formula t) = Mixfix_formula t'
     where t' = homomorphy_term t