search(X, X, T).
search(X, Y, T) :- (edge(X, Z); edge(Z, X)),
                   not(member(Z, T)),
                   search(Z, Y, [Z|T]).

member(X, [X|_]) :- !.
member(X, [_|Y]) :- member(X, Y).

edge(g,h).    edge(g,d).     edge(e,d).      edge(h,f).     edge(e,f).
edge(a,e).    edge(a,b).     edge(b,f).      edge(b,c).     edge(f,c).