How to calculate the distance between two cities??

[inuy]

How to calculate the distance between two
cities more than one city away from each other (by direct
connection).
distance(brisbane, sydney, 1000).
distance(sydney, canberra, 400).
distance(canberra, toowoomba, 1200).
distance(toowoomba, brisbane, 200).

for example:
one city away form each other.
oad(X, Y, D) :-
distance(X, Z, D1),
distance(Z, Y, D2),
D is D1+D2.

 

[slackerbrad]

You should throw in a recursive step. i.e. add:

oad(X,Y,D) :- distance(X,Y,D). {base case}
oad(X,Y,D) :-
distance(X,Z,D1),
oad(Z,Y,D2),
D is D1+D2.

 

[MelaOS]

Now that the first step is out of the way, is there any way to refine the recursion so that it can filter out some certain place?

let's say that the journey shouldn't past through canberra,and we add another route to it like:

(sydney,disneyland).
(disneyland,toowomba).

Please help!!>!??!