Assertion: chess set's piece | /r/HasProperty | undefended
Facets:
Source sentences:
text: Attacking a piece usually, but not always (see Sacrifice), forces the opponent to respond if the attacked piece is undefended, or if the attacking piece is of lower value than the one attacked.
text: However, a queen fork is only useful if both pieces are undefended, or if one is undefended and the other is the enemy's king.
text: The introduction of the 'extra' move by the third player can introduce situations of deadlock, for example, if a white piece is undefended and simultaneously attacked by both black and red pieces.