Full Idea
If we stipulate that 'x is heterological' iff it does not apply to itself, we speedily arrive at the contradiction that 'heterological' is itself heterological just in case it is not.
Gist of Idea
If 'x is heterological' iff it does not apply to itself, then 'heterological' is heterological if it isn't heterological
Source
B Hale / C Wright (Intro to 'The Reason's Proper Study' [2001], 3.2)
Book Reference
Hale,B/Wright,C: 'The Reason's Proper Study' [OUP 2003], p.18