considered as a circular function.

1. Press to start the drawing of the graph.
2. Press any key to suspend the drawing; then the pressing of any key will resume the drawing. There is no way to stop the drawing and start over from the beginning without killing the program.
3. After the graph has been drawn, you can press
   • to clear the graph,
   • to redraw the graph but you should press first,
   • to decrease the delay in the drawing of the graph,
   • to make the drawing of the graph slower, and
   • to quit the program.