General
Material
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5

Solution

travel(X,Y,go(X,Y,Transport)) :- onestep(X,Y,Transport).
travel(X,Y,go(X,Z,Transport,Path)) :- onestep(X,Z,Transport),
                            travel(Z,Y,Path).

onestep(X,Y,byCar) :- byCar(X,Y).
onestep(X,Y,byTrain) :- byTrain(X,Y).
onestep(X,Y,byPlane) :- byPlane(X,Y).
    

Back to the exercise.