Version 1: UFO moves down, and the cow stays still.

Version 2: The UFO's can be controlled horizontally with keys.

Version 3: The ufo can collide with the cow.  The cow is at a fixed,
random position.

Version 4: Derived from version 1.  The cow moves from right to left,
and the ufo can move straight down.

Version 5: Added keyboard control back to the ufo as well as collision
against the cow.

Version 6: There are now multiple cows.

Version 7: The cows can now also move from left to right as well as
right to left.

Version 8: Cows can collide with each other or edges of the scene, in
which case they change direction.



Solutions [password protected (why?)]