The university employs 3,401 full-time faculty members across its eleven schools, including 18 members of the National Academy of Sciences, 65 members of the American Academy of Arts and Sciences, 19 members of the National Academy of Engineering, and 6 members of the Institute of Medicine. Notable faculty include 2010 Nobel Prize–winning economist Dale T. Mortensen; nano-scientist Chad Mirkin; Tony Award-winning director Mary Zimmerman; management expert Philip Kotler; King Faisal International Prize in Science recipient Sir Fraser Stoddart; Steppenwolf Theatre director Anna Shapiro; sexual psychologist J. Michael Bailey; Holocaust denier Arthur Butz; Federalist Society co-founder Steven Calabresi; former Weatherman Bernardine Rae Dohrn; ethnographer Gary Alan Fine; Pulitzer Prize–winning historian Garry Wills; American Academy of Arts and Sciences fellow Monica Olvera de la Cruz and MacArthur Fellowship recipients Stuart Dybek, and Jennifer Richeson. Notable former faculty include political advisor David Axelrod, artist Ed Paschke, writer Charles Newman, Nobel Prize–winning chemist John Pople, and military sociologist and "don't ask, don't tell" author Charles Moskos.

Answer this question, if possible (if impossible, reply "unanswerable"): Who is Southwestern's faculty member notable for being a Holocaust denier?
unanswerable