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# ?X &< ?Y

X is before Y in the domain order

X
  variable or domain value
Y
  variable or domain value

## Description

Constrains X and Y such that X is before Y in the domain order. X and Y must be variables or values of the same domain. If one of them is domain-less, it will be given the same domain as the other.

### Modules

This predicate is sensitive to its module context (tool predicate, see @/2).

## Examples

        ?- [X,Y] &:: weekday, X &< Y.
        X = X{[mo, tu, we, th, fr, sa]}
        Y = Y{[tu, we, th, fr, sa, su]}
        There is 1 delayed goal.
        Yes (0.00s cpu)

        ?- mo &< th.
        Yes (0.00s cpu)

        ?- X &< th.
        X = X{[mo, tu, we]}
        Yes (0.00s cpu)

        ?- fr &< th.
        No (0.00s cpu)

        ?- X &< Y.
        Arguments have no domains in X &< Y in module eclipse
        Abort

        ?- X &:: weekday, X &< red.
        Arguments have different domains (weekday,colour) in X &< red ...
        Abort

## See Also

&< / 3, &> / 2, &=< / 2, &>= / 2, &= / 2, &\= / 2, shift / 3, rotate / 3, domain / 1