65. A problem about mattress turning is that people usually don’t remember the immediately previous position or immediately previous turn that they made months ago. So the next time, they could wind up just turning the mattress back to the position that it was in only two seasons ago. Show that the mnemonic “Spin in spring, flip in fall” (courtesy of Bill Sandidge of Atlanta, Georgia), in fact, cycles the mattress through its four positions.
65.
The notation of Example 6 uses for flip, (rotation) for spin. Start in summer in the upper left position of the figure for Example 6 and follow the arrows: The in the fall brings the mattress to the position in the upper right, following that by takes it to the position in the lower left, doing another brings it to the position in the lower right, and yet another brings it back to the original position at upper left.