IN Fig. 6, Q C is the extra link pivoted to the fixed point Q, the other pivot on it C, describing the circle OCR. The straight lines? ? and F M' are supposed to be perpendicular to M R Q M'. You have ...

Linus is using a thin felt-tip pen and a ruler to draw straight lines on a conventional 8×8 chessboard. With eight lines, he can easily ensure that a line passes through every square on the board. For ...