Diamonds can be found either lying around, or manufactured from crushing the lighter coloured boulders together. The darker @-filled bolders cannot be crushed into diamonds, only moved around.
To move around use the h,j,k and l keys.
There is a save and load feature which can be invoked using S and L keys. The
save file is $HOME/cod.save. (This is one of the less buggy features of the
game - so please make good use of it)
To quit and restart a level, press 'q'. To redraw the screen, press control L.
To exit the game press control C (or interrupt).
The start level is level number 0. To start on another level simply state the number as the first (and only) argument to perp.
There are no checks on which levels exist. If you attempt to start on a non existant level then the game will simply go loopy. This will also happen upon finishing the last level.
Also, the level argument can be supplied as a negative number. This, also understandably causes a few worried looks from the program. If you try harder then it'll probably just have a nervouse breakdown and burst into tears with a segmentation fault.
Very little (in fact none) integrity checking is done on the map and sprite data files read in by the game.