In 1993, Dutch chess problem composer R. Bosma noted in the FIDE-rules article 9.1, which stated:
The King is in check when the square on which it is standing is attacked by one or two enemy pieces.Thus from this rule, it appears that a king is not in check when its square is attacked three or more times. This inspired Bosma to the following fairy chess form, called Bosma chess:
A king that is attacked three or more times is not considered to be in check.The rule is used in some fairy chess problems; in actual games, there would be little difference with standard chess.
Bosma Chess. White to mate in two moves.
The FIDE rules have since been adjusted.