==> real-life/icecubes.s <==
By using frozen cubes as spacers to hold the trays apart, you can make
84 cubes in the time it takes to freeze two trays.  Fill one tray,
freeze it and remove the cubes.  Place two cubes in the opposite
corners of six trays, and fill the rest with water.  Freeze all six,
plus a seventh you put on top, at the same time.