[ library(cardinal) | Third Party Libraries | Reference Manual | Alphabetic Index ]

# ?Element `@ ?SetVariable

Set membership constraint

SetVariable
  A set variable.
Element
  A ground term or a variable.

## Description

Constrain SetVariable to include Element.

If Element is a variable then if SetVariable is a ground singleton, then Element is unified with its single element, otherwise the constraint is suspended until Element or SetVariable is ground.

### Fail Conditions

Fails if Element can not be a member of SetVariable.

### Resatisfiable

No.

## Examples

    ?- S `:: []..[a,b], a `@ S, glb_poss(S,G,P).
    G = [a], P = [b]

    ?- S `:: []+[a,b], c `@ S.
    no

    ?- S `:: [a]+[b,c], a `@ 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 = [b], P = [a]

    ?- S `:: [a]+[b,c]:C, X `@ S, C=1.
    X = a

## See Also

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