
			HOW TO PROVE IT, PART 4

proof by personal communication:
	'Eight-dimensional colored cycle stripping is NP-complete 
	[Karp, personal communication].' 

proof by reduction to the wrong problem:
	'To see that infinite-dimensional colored cycle stripping is 
	decidable, we reduce it to the halting problem.' 

proof by reference to inaccessible literature:
	The author cites a simple corollary of a theorem to be found 
	in a privately circulated memoir of the Slovenian 
	Philological Society, 1883.

proof by importance:
	A large body of useful consequences all follow from the 
	proposition in question.
