direct_route(ithaca, syracuse).
direct_route(syracuse, orlando).
direct_route(ithaca, nyc).
direct_route(syracuse, nyc).
direct_route(syracuse,  sanfrancisco).
direct_route(syracuse, boston).
travel(A,B) :- direct_route(A, B).
     travel(A,B) :- direct_route(A, C),
                     travel(C,B).