free_term (Application os ts r) = Application os' ts' r
     where ts' = map free_term ts
           os' = free_op_sym os
free_term (Application os ts r) = Application os' ts' r
     where ts' = map free_term ts
           os' = free_op_sym os
free_term (Application os ts r) = Application os' ts' r
     where ts' = map free_term ts
           os' = free_op_sym os