Copyright (1997) American Association of Physics Teachers. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Association of Physics Teachers.

The following article appeared in F. J. Duarte, Interference, diffraction, and refraction, via Dirac's notation, Am. J. Phys. 65, 637-640 (1997) and may be found at http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000065000007000637000001&idtype=cvips&gifs=Yes

Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.