Equivalent to BX #= (ConX), BY #= (ConY), Bool #= (BX #= BY)
The two constraints are reified in such a way that Bool is true if ConX and ConY have the same truth value. ConX and ConY must be constraints that have a corresponding reified form.
This reified connective is not available in IC because #=/3 can be used instead. It is provided in GFD as <=> maps 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.
A more restricted version of this constraint is defined in the global constraint catalog as 'equivalent', in that the reified truth value is the logical equivalence of 0/1 variables rather than constraints.