This chapter implements an interactive, graphical version of the "guess my
numbers" game. Open the file

	 source.rkt 

in DrRacket. The instructions for starting are at the top of the file. 
Our tests are at the bottom of the file in a separate 'test' submodule. 

;; -----------------------------------------------------------------------------

If you wish to experiment with a small world program, open 

         ufo-source.rkt

The file runs a UFO from the top of the screen to the bottom.