Equivalent to BX #= (ConX), BY #= (ConY), BX + BY #= 2
The two constraints are reified in such a way that both must be true. ConX and ConY must be a constraints that have a corresponding reified form.
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.