Just predicatesSample answers

Here is a formulation of “Four Trees” using predicates only – that is, without function symbols. For this particular problem, it is quite natural to express the constraints in this way, and it is certainly closer to first order logic as standardly taught in logic courses. Note, however, that we have to give axioms carefully specifying the logical properties of our relations: we can’t just rely on the positions of the trees to be all different and numerically ordered as we did when using the function symbol.