棋盘覆盖问题：在一个2^k*2^k个方格组成的棋盘中用4种不同形态的L型骨牌覆盖一个给定的特殊棋盘上除特殊方格以外的所有方格，且任何2个L型骨牌不得重叠覆盖-Board cover: a chessboard 2 ^ k* 2 ^ k squares composed using four kinds of different forms of an L-type domino covering all given special squares on the board except for