free_term (Mixfix_qual_pred ps) = Mixfix_qual_pred ps'
     where ps' = free_pred_sym ps
free_term (Mixfix_qual_pred ps) = Mixfix_qual_pred ps'
     where ps' = free_pred_sym ps
free_term (Mixfix_qual_pred ps) = Mixfix_qual_pred ps'
     where ps' = free_pred_sym ps