decrement the number of values b that support the assignment v1=x ie: b
such that v1=x, v2=b is a feasible pair When this count reaches 0,
discard the value x from the domain of v1.
two methods used for detecting that an edge should be removed from the bipartite assignment graph
deleteMatch -> removes it from the graph data strutures
deleteEdgeAndPublish -> same + publishes the information outside the constraint
A heuristic selecting the IntDomainVarImpl with smallest ration (domainSize / degree)
(the degree of a variable is the number of constraints linked to it)