def back_rank_mate(puzzle: Puzzle) -> bool:
node = puzzle.game.end()
board = node.board()
king = board.king(not puzzle.pov)
assert king is not None
assert isinstance(node, ChildNode)
back_rank = 7 if puzzle.pov else 0
if board.is_checkmate() and square_rank(king) == back_rank:
squares = SquareSet.from_square(king + (-8 if puzzle.pov else 8))
if puzzle.pov:
if chess.square_file(king) < 7:
squares.add(king - 7)
if chess.square_file(king) > 0:
squares.add(king - 9)
else:
if chess.square_file(king) < 7:
squares.add(king + 9)
if chess.square_file(king) > 0:
squares.add(king + 7)
for square in squares:
piece = board.piece_at(square)
if piece is None or piece.color == puzzle.pov or board.attackers(
puzzle.pov, square):
return False
return any(
square_rank(checker) == back_rank for checker in board.checkers())
return False
def exposed_king(puzzle: Puzzle) -> bool:
if puzzle.pov:
pov = puzzle.pov
board = puzzle.mainline[0].board()
else:
pov = not puzzle.pov
board = puzzle.mainline[0].board().mirror()
king = board.king(not pov)
assert king is not None
if chess.square_rank(king) < 5:
return False
squares = SquareSet.from_square(king - 8)
if chess.square_file(king) > 0:
squares.add(king - 1)
squares.add(king - 9)
if chess.square_file(king) < 7:
squares.add(king + 1)
squares.add(king - 7)
for square in squares:
if board.piece_at(square) == Piece(PAWN, not pov):
return False
for node in puzzle.mainline[1::2][1:-1]:
if node.board().is_check():
return True
return False