Suggested modificatin to AC-3 (aima3e Figure 6.3)

[ctjoreilly]

In the paragraph before section 6.2.1, leading up to the AC-3 algorithm's description, it states 'If we treat each variable as a node in a graph (see Figure 6.1(b)) and each binary constraint as an arc...' implies there is a one to one mapping between arcs and binary constraints. However, arcs as described in the original paper (http://www.cs.ubc.ca/~mack/Publications/AI77.pdf) are directional while the constraints/relations are un-directed (requiring two arcs for each binary constraint to be considered in the logic). This distinction is important as without it, if arcs for each direction of a binary constraint are not added, the AC-3 algorithm will fail to make the whole CSP arc-consistent.

[norvig]

So, your suggestion is "... each binary constraint as two arcs (one in each direction) ..."?

[ctjoreilly]

Yes.