---------------------------------------
A B C D E F G H

Diag. 2.

If a player succeeds in reaching the eighth rank with one of his
pawns he is entitled to call for any piece of higher grade, with
the exception of the King, in place of such pawn.

Each move in a game of chess consists of the displacement of one
piece only, with the exception of what is termed "castling," in
which the King and either Rook can be moved simultaneously by
either player once in a game. In castling, the King moves
sideways to the next square but one, and the Rook to which the
King is moved is placed on the square which the King has skipped
over. Castling is only allowed if neither the King nor the Rook
concerned have moved before, and if there is no piece between the
Rook and King.

Diagram 3 shows a position in which White has castled on the
Queen's side, and Black on the King's side. Castling is not
permitted if the King in castling must pass over a square
attacked by a hostile piece. A square (or a piece) is said to be
"attacked" when the square (or the piece) is in the line of
action of a hostile unit. A square (or a piece) is said to be
covered or protected if an opposing piece occupying that square
(or capturing the piece) could itself be captured.

When attacking the King it is customary to call "check," to
notify the opponent of the fact; for the attack on the King