Prolog Algorithm

I am in need of completing a path finding (astar) algorithm in SWI Prolog. The algorithm is pretty simple, you just choose the next edge based on the next shortest path (factoring in a straight line distance heuristic to the edge where this function/rule is provided), but the recursive nature of prolog and creating rules makes it more of a challenge. There is psuedo code, notes, and a prolog graph configuration prolog file. There are also several stubs for the entry point, notes on the start state configuration structure and several slides. The assignment is just to implement the remaining rules commented by psuedo code which is estimated at 40 lines of code left. I am thinking an experienced prolog programmer could knock this out in an hour or so.