graphplan.pl returns the same plan multiple times

[fgaignier]

Hello,

I have been downloading and trying your graphplan implementation with the rocket_plan example.
But unfortunately it returns thesame plan so many times. For instance test(P) returns the same plan about 20 times (or more):

?- test(P).
P = [[load(rocket1, london, a)], [move(rocket1, london, paris)], [unload(rocket1, paris, a)]] ;
P = [[load(rocket1, london, a)], [move(rocket1, london, paris)], [unload(rocket1, paris, a)]] ;
P = [[load(rocket1, london, a)], [move(rocket1, london, paris)], [unload(rocket1, paris, a)]] ;
P = [[load(rocket1, london, a)], [move(rocket1, london, paris)], [unload(rocket1, paris, a)]] ;
P = [[load(rocket1, london, a)], [move(rocket1, london, paris)], [unload(rocket1, paris, a)]] ;

I am using swipl Vesrion 7.2.3

Any idea what could cause this?

Thank you for your help

Fabrice