Multi tool use

Prolog Special Path Finding

I'm new to Prolog and I'm struggling doing a task. So, we have 2 types of edges, one for car and one for bus. They are symmetrical. There is no distance, just direction. For example:

car(berlin, munich).
car(berlin, stuttgart).
car(mainz, munich).

bus(augsburg, berlin).
bus(köln, dortmund).
bus(dortmund, stuttgart).


My task is to find if there is a path between a 'Start' and 'End Location', which has been resolved but now comes the "hard" part. We have to find a path that changes max ONE time between bus and car. Also if I'm in a bus I have to get to my end location just within buses or change one time the bus with a car(of course we can then change between cars, but not back to bus).

Also I've found a way to find the path but just for bus paths, not cars and it looks like this.

isPath(from, to) :- isPath(from, to, ).
isPath(from, to, _) :- bus(from, to).
isPath(from, to, visited) :-
+ member(from, visited),
bus(from, X),
isPath(X, to, [from|visited]).


I'm sure it is not that hard, I just have to save somehow the fact that the bus/car has been changed with the other one.

Can someone help me?

Thanks!

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