Nine Dots Puzzle

On a piece of paper, draw 9 dots in the shape of a square. The challenge is to trace through all of the 9 dots using just 4 straight lines, without lifting the pen from the paper. This is literally thinking outside the box. This trace perfect puzzle mimics the 9 dot puzzle. The lines are invisible until you traverse them.
See Also: http://en.wikipedia.org/wiki/Thinking_outside_the_box

link to this puzzle