[eclipse-clp-users] basic problem

Hello everyone,

I'm totally new to ECLiPSe, and set out to solving rather silly problem 
purely for sake of learning: find a minimum sum of 6 integers, all 
different, with each integer belonging to a given range.

:- lib(ic).
:- lib(branch_and_bound).

minsum(X, Range) :-
     X = [A,B,C,D,E,F],
     X :: 1 .. Range,
     integers(X),
     alldifferent(X),
     bb_min(sum(X,S),S),
     labeling(X).

However, I get:

calling an undefined procedure bb_min(sum([_313, _331, _349, _367, _385, 
_403], _612), _612) in module eclipse

How come? After all, I do use relevant branch_and_bound library?

Regards,
mk