Combat requirements

[MedeaMelana]

Certain cards say that a creature must attack, must block, or must be blocked (Courtly Provocateur, Reckless Brute, Predatory Rampage). Furthermore, if combat requirements would conflict with combat restrictions (things that say "can't"), all restrictions must be obeyed, and as many requirements must be obeyed as possible.

At the moment I don't know how to implement this efficiently, i.e. faster than 2^n, where n is the number of creatures involved.