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# <ConsistencyModule:> +ConX <=> +ConY

Constraint ConX has the equivalent truth value as ConY.

ConX
  Constraint
ConY
  Constraint

## Description

Equivalent to BX #= (ConX), BY #= (ConY), BX #= BY

The two constraints are reified in such a way that ConX and ConY constrained to the same truth value. ConX and ConY must be constraints that have a corresponding reified form.

This connective is not available in IC because #=/2 can be used instead. It is provided in GFD as it maps directly to gecode's equivalence connective.

ConsistencyModule is the optional module specification to give the consistency level for the propagation for this constraint: gfd_bc for bounds consistency, and gfd_gac for domain (generalised arc) consistency.

This constraint is implemented using Gecode's MiniModel's rel() for both integer and boolean expressions, with sub-expressions/constraints not supported by MiniModel factored out and posted as auxiliary constraints.

### Modules

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

## See Also

<=> / 3, neg / 1, or / 2, xor / 2, and / 2, => / 2, suspend : #= / 2, ic : #= / 2, fd : #= / 2