This is necessary to actually take the new value into account. Example: ?- sat(A*B>=C*D), A=1,B=0,C=1,D=1. false. This addresses #670.
Examples: ?- taut(X=:=X,1). clpb:sat(X=:=X) ; false. ?- taut(X=\=X,0). clpb:sat(X=:=X) ; false.