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# ?C1 #<=> ?C2

The constraint expression C1 is equivalent to the constraint expression C2.

?C1
  An arithmetic constraint expression.
?C2
  An arithmetic constraint expression.

## Description

This constraint states that the constraint expressions C1 and C2 evaluate to the same truth value, either both true of both false. If this is already the case, it simply succeeds. Otherwise it is suspended and after each domain change that may cause one of the constraint expressions to succeed to fail, it is woken and and re-evaluated. Subsequently, if one of the constraint expressions is true or false, the same truth value is imposed on the other one.

### Fail Conditions

Fails if C1 and C2 are not bothe true or both false.

### Resatisfiable

No.

## See Also

#\/ / 2, #/\ / 2, #=> / 2, #\+ / 1