First move a unit on a white square, then move a unit on a black square. If either is not possible, that portion of turn is lost. Castle at either time. Check on the first move deprives you of your second move. You must defend against check on your first move, and if this involves a move from a black square, the move from the white square is lost.
These are simple illustrations rather than strong opponents.
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Written by Ed Friedlander
