Use constraints to build set union of finite sets of positive natural numbers

Help! Data Structure
2

The ins/2 constraint doesn’t apply to a list variable, it applies the constraint to members of that list. Also, you are confusing domains with the variable they represent, you can use fd_dom/2 to query a variables domain .

Without knowing exactly what you are trying to do, here is some sample code that may provide insight.

?- X in 1..5, Y in 3..8, Z = [X,Y], Z = [H|T], fd_dom(H,FirstDom), foldl([I,C,O]>>(fd_dom(I,Range),O = C\/Range),T,FirstDom,Union),K in Union.
X = H,
Z = [H, Y],
T = [Y],
FirstDom = 1..5,
Union = 1..5\/3..8,
H in 1..5,
Y in 3..8,
K in 1..8.
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