Prolog is pretty unique. I’ve run into similar frustrations when I have used it as well. I think you have to drop all your preconceived notions and past programming experience when you use Prolog and just accept it as it is. Prolog was developed to run in very small machines and so the resolution algorithm operates in a strict order. This means clause order sometimes matters. Overall, I’ve found it useful to always keep in mind that I’m unifying trees of terms, not so much programming in a pure logical language.