?-use_module(library(lists)).
edge(a,b). edge(b,c).  edge(a,c).  edge(c,e). edge(b,f).  edge(b,e).  edge(d,f).
edge(f,g).  edge(g,h).  edge(f,j).  edge(j,k).  edge(e,g).
goal(k).
goal(g).


breadthFirst(In,[Z]):- setof(X,(member(X,In),goal(X)),Z), Z\=[], !.
breadthFirst(In,[U,V|W]):- 
     setof(Y, X^(member(X,In), edge(X,Y)),Set),
     breadthFirst(Set,[V|W]), 
     setof(Son, Parent^(member(Parent,V), edge(Son,Parent),member(Son,In)), U).

?-breadthFirst([a,b],X), print(X), nl.