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**Underwood Dudley** (born January 6, 1937) is an American
mathematician. His popular works include several books describing
crank mathematics by
pseudomathematicians who incorrectly believe they have
squared the circle or done other impossible things.

Dudley was born in
New York City. He received
bachelor's and
master's degrees from the
Carnegie Institute of Technology and a
PhD from the
University of Michigan. His academic career consisted of two years at
Ohio State University followed by 37 at
DePauw University, from which he retired in 2004. He edited the *
College Mathematics Journal* and the *Pi Mu Epsilon Journal*, and was a Pólya Lecturer for the
Mathematical Association of America (MAA) for two years. He is the discoverer of the
Dudley triangle.

Dudley's popular books include *
Mathematical Cranks* (MAA 1992,
ISBN
0-88385-507-0), *The Trisectors* (MAA 1996,
ISBN
0-88385-514-3), and *Numerology: Or, What Pythagoras Wrought* (MAA 1997,
ISBN
0-88385-524-0). Dudley won the
Trevor Evans Award for expository writing from the MAA in 1996.

Dudley has also written and edited straightforward mathematical works such as *Readings for Calculus* (MAA 1993,
ISBN
0-88385-087-7) and *Elementary Number Theory* (W.H. Freeman 1978,
ISBN
0-7167-0076-X). In 2009, he authored "A Guide to Elementary Number Theory" (MAA, 2009,
ISBN
978-0-88385-347-4), published under Mathematical Association of America's Dolciani Mathematical Expositions.

In 1995, Dudley was one of several people sued by William Dilworth for
defamation because *Mathematical Cranks* included an analysis of Dilworth's "A correction in set theory",^{
[1]} an attempted refutation of
Cantor's diagonal method. The suit was dismissed in 1996 due to failure to state a claim.

The dismissal was upheld on appeal in a decision written by jurist
Richard Posner. From the decision: "A
crank is a person inexplicably obsessed by an obviously unsound idea—a person with a bee in his bonnet. To call a person a crank is to say that because of some quirk of temperament he is wasting his time pursuing a line of thought that is plainly without merit or promise ... To call a person a crank is basically just a colorful and insulting way of expressing disagreement with his master idea, and it therefore belongs to the language of controversy rather than to the language of defamation."^{
[2]}

**^**Dilworth, William (1974), "A correction in Set Theory" (PDF),*Transactions of the Wisconsin Academy of Sciences, Arts and Letters*,**62**: 205–216, retrieved June 16, 2016**^**Caselaw: United States Court of Appeals, Seventh Circuit, ruling on Dillworth vs. Dudley, 1996

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Underwood Dudley**.