Element constraint
(accessing the ith element in a list of values, where i is a variable)
the slot v0 represents the index and the slot v1 represents the value
propagation with complete arc consistency from values to indices (v1 to v0)
propagation with interval approximation from indices to values (v0 to v1)
Propagation:
Computes consistency on the problem (the problem may no longer
be consistent since the last propagation because of listeners
that have been posted and variables that have been reduced
propagates the constraint sigma(ai Xi) + c <= 0 where mylb = sigma(ai inf(Xi)) + c
note: this does not reach saturation (fix point),
but returns a boolean indicating whether it infered new information or not.
propagates the constraint sigma(ai Xi) + c <= 0 where myub = sigma(ai sup(Xi)) + c
note: this does not reach saturation (fix point),
but returns a boolean indicating whether it infered new information or not.