Have you been exposed to more recent research on Prolog language constructs? In particular, I recommend the following publication: https://arxiv.org/abs/1607.

Have you been exposed to more recent research on Prolog language constructs? In particular, I recommend the following publication: https://arxiv.org/abs/1607.01590 https://arxiv.org/abs/1607.01590 if_/3 and other declarative predicates like dif/2 are more general alternatives and likely good solutions in the cases you mention. They are still quite recent, at least if we ignore the fact that dif/2 was even available in the very first Prolog system, sometimes called Prolog 0.