Changed queue to set in AC3 (as in the pseudocode of the original algorithm) to reduce the number of consistency-check due to the redundancy of the same arcs in queue. For example, on the harder1 configuration of the Sudoku CSP the number consistency-check has been reduced from 40464 to 12562!

AC3 algorithm has non-optimal worst case time-complexity O(cd^3 ), while AC4 algorithm runs in O(cd^2) worst case time

…he constant propagation algorithm in mac inference

…eady present in test_csp.py

This reverts commit 20ab0e5.

This reverts commit f743146.

This reverts commit 9e0fa55.

… are already present in test_csp.py"

This reverts commit b3cd24c.

…oosing the constant propagation algorithm in mac inference"

This reverts commit 6986247.

This reverts commit 03551fb.

This reverts commit 93af259.

This reverts commit 6641c2c.