If SetVar2 is not yet a set domain variable it is declared as such, using SetVar1's lub.
?- [7,8,9] `>= [7,9], [7,8,9] `>= [7,8,9], [7,8,9] `>= [], [7,8,9] `>= [9]. yes ?- [1,7,9] `>= [7,8]. no ?- X `:: [a]+[b,c,d], Y `:: []+[a,b,c,d,e,f], X `>= Y, poss(Y,PY). PY = [a,b,c,d] ?- X `:: [a]+[b,c,d], Y `:: []+[a,b,c,d,e,f], Y `>= X, glb(Y,GY). GY = [a] ?- X `:: [a]+[b,c,d,z]:CX, Y `:: []+[a,b,c,d,e,f]:CY, X `>= Y, CX=2, fd:maxdomain(CY,MaxCY). MaxCY = 2 ?- X `:: [a]+[b,c,d,z]:CX, Y `:: []+[a,b,c,d,e,f]:CY, X `>= Y, CY=3, fd:mindomain(CX,MinCX). MinCX = 3.