Simple graph search in Prolog

Question

I\'m trying to code a simple graph search in SWI-Prolog. I came up with the following program:

adjacent(1,4). adjacent(4,2). adjacent(3,6).
adjacent(6,4). ad         


        

Answer 1

The main problem here is the member test: the signature is member(Element,List); you seem to assume that the arguments are the other way 'round.

In addition, your first path predicate is meant to test a two-element list, however, B really unifies with the rest list (which then isn't connected).

If you fix these, you find that this can only work for fully instantiated variables, as the negation doesn't work well for unbound variables.