Tom: I bet I can make you say purple.
Joe: How?
Tom: What colors are in the American flag?
Joe: Red, white and blue.
Tom: I told you I can make you say red.
Joe: You said purple!
Tom: I told you I could make you say purple!
Three: one to write the light bulb removal program, one to write the light bulb insertion program, and one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.