ADDED: CLP(B): Tentative version of sat(card(Is,Fs)),
       constraining the number of true expressions in the list Fs to
       be a member of the list of integers Is.

         Example:

             ?- sat(card([2],[X,X*Y,Z])), labeling([X,Y,Z]).
             %@ X = Z, Z = 1, Y = 0 ;
             %@ X = Y, Y = 1, Z = 0.