Find set of solutions and terminate in SWI-Prolog?

Question

Here is my program:

reachable(X) :- start(X).
reachable(X) :- link(Y, X), reachable(Y).

start(london).

link(london, paris).
link(paris, london).
link(london, berlin).
link(paris, berlin).
link(berlin, paris).

Now if I query it, I get solutions:

?- reachable(X).
X = london ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
X = paris ;
...

Why does SWI-Prolog keep finding the same solutions?

How can I fix my program to return the set of solutions then halt?

Here's what I am looking for:

?- reachable(X).
X = paris ;
X = london ;
X = berlin ;
No

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$ swipl --version  
SWI-Prolog version 7.6.4 for amd64