directTrain(forbach,saarbruecken).
    directTrain(freyming,forbach).
    directTrain(fahlquemont,stAvold).
    directTrain(stAvold,forbach).
    directTrain(saarbruecken,dudweiler).
    directTrain(metz,fahlquemont).
    directTrain(nancy,metz).
    
    
train(X,Y):-directTrain(X,Y).
train(X,Y):-directTrain(Y,X).


travelBetween(X,Y):-train(X,Y).
travelBetween(X,Y):-train(X,Z),not(Z=Y),
    travelBetween(Z,Y).