GNU Go Documentation
9.5.1 Attacking and defending moves
A move which tactically captures a worm is called an attack move and a
move which saves a worm from being tactically captured is called a
defense move. It is understood that a defense move can only exist if
the worm can be captured, and that a worm without defense only is
attacked by moves that decrease the liberty count or perform necessary
backfilling.
It is important that all moves which attack or defend a certain string
are found, so that the move generation can make an informed choice
about how to perform a capture, or find moves which capture and/or
defend several worms.
Attacking and defending moves are first found in make_worms while it
evaluates the tactical status of all worms, although this step only
gives one attack and defense (if any) move per worm. Immediately
after, still in make_worms, all liberties of the attacked worms are
tested for additional attack and defense moves. More indirect moves
are found by find_attack_patterns and find_defense_patterns,
which match the A (attack) and D (defense) class patterns in
`patterns/attack.db' and `patterns/defense.db' As a final step, all
moves which fill some purpose at all are tested whether they additionally
attacks or defends some worm. (Only unstable worms are analyzed.)
