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# ?Element `-@ ?SetVariable

Set non-membership constraint
*SetVariable*
- A set variable.
*Element*
- A ground term or a variable.

## Description

Constrain SetVariable to not include Element.
If Element is a variable then the constraint
is suspended until it becomes ground.

### Fail Conditions

Fails if Element must be a member of SetVariable.
### Resatisfiable

No.
## Examples

?- S `:: []..[a,b], a `-@ S, glb_poss(S,G,P).
G = [], P = [b]
?- S `:: [c]+[a,b], c `-@ S.
no
?- S `:: [a]+[b,c], z `-@ S, glb_poss(S,G,P).
G = [a], P = [b,c]
?- S `:: []..[a,b], X `-@ S, glb_poss(S,G,P).
G = [], P = [a,b]
?- S `:: []..[a,b], X `-@ S, X=b, glb_poss(S,G,P).
G = [], P = [a]

## See Also

`@ / 2, in / 2, notin / 2, `:: / 2