Difference between AC-1 and AC-3 algorithm?

Question

I am trying to understand both algorithms but can't find the difference between them.

http://en.wikipedia.org/wiki/AC-3_algorithm

Answer 1

You're right that both algorithms have the same iterate-to-fixed-point structure. The difference is that AC-3 uses a data structure to avoid processing arcs whose endpoint domains haven't changed since the last time they were processed – such processing would accomplish nothing.