63 Methods of Mathematical Proof


If the proof of a theorem is not immediately apparent, it may be because you are trying the wrong approach. Below are some effective methods of proof that may aim you in the right direction.

  1. Proof by Obviousness: "The proof is so clear that it need not be mentioned."
  2. Proof by General Agreement: "All in Favor?..."
  3. Proof by Imagination: "Well, We'll pretend its true."
  4. Proof by Convenience: "It would be very nice if it were true, so ..."
  5. Proof by Necessity: "It had better be true or the whole structure of mathematics would crumble to the ground."
  6. Proof by Plausibility: "It sounds good so it must be true."
  7. Proof by Intimidation: "Don't be stupid, of course it's true."
  8. Proof by Lack of Sufficient Time: "Because of the time constraint, I'll leave the proof to you."
  9. Proof by Postponement: "The proof for this is so long and arduous, so it is given in the appendix."
  10. Proof by Accident: "Hey, what have we here?"
  11. Proof by Insignificance: "Who really cares anyway?"
  12. Proof by Mumbo-Jumbo: " For any epsilon> 0 there exists a corresponding delta > 0 s.t. f(x)-L < epsilon whenever x-a < delta"
  13. Proof by Profanity: (example omitted)
  14. Proof by Definition: "We'll define it to be true."
  15. Proof by Tautology: "It's true because it's true."
  16. Proof by Plagiarism: "As we see on page 238 ..."
  17. Proof by Lost Reference: "I know I saw this somewhere ..."
  18. Proof by Calculus: "This proof requires calculus, so we'll skip it."
  19. Proof by Terror: When intimidation fails ...
  20. Proof by Lack of Interest: "Does anyone really want to see this?"
  21. Proof by Illegibility: " ¥ ª Ð Þ þæ"
  22. Proof by Logic: "If it is on the problem sheet, then it must be true."
  23. Proof by Majority Rule: Only to be used if General Agreement is impossible.
  24. Proof by Clever Variable Choice: "Let A be the number such that this proof works."
  25. Proof by Tessellation: "This proof is just the same as the last."
  26. Proof by Divine Word: "And the Lord said, 'Let it be true,' and it came to pass."
  27. Proof by Stubbornness: "I don't care what you say! It is true!"
  28. Proof by Simplification: "This proof reduces to the statement, 1 + 1 = 2."
  29. Proof by Hasty Generalization: "Well, it works for 17, so it works for all reals."
  30. Proof by Deception: "Now everyone turn their backs ..."
  31. Proof by Supplication: "Oh please, let it be true."
  32. Proof by Poor Analogy: "Well, it's just like ..."
  33. Proof by Avoidance: Limit of Proof by Postponement as t approaches infinity.
  34. Proof by Design: "If it's not true in today's math, invent a new system in which it is."
  35. Proof by Intuition: "I just have this gut feeling ..."
  36. Proof by Authority: "Well, Bill Gates says it's true, so it must be."
  37. Proof by Vigorous Assertion: "And I REALLY MEAN THAT!"
  38. Proof by A.F.K.T. Theorem: "Any Fool Knows That!"
  39. Proof by Divine Intervention: "Then a miracle occurs ..."
  40. Proof by Example: "The author gives only the case n = 2 and suggests that it contains most of the ideas of the general proof."
  41. Proof by Intimidation:  "Trivial"
  42. Proof by Vigorous Handwaving: "Works well in a classroom or seminar setting."
  43. Proof by Cumbersome Notation: "Best done with access to at least four alphabets and special symbols."
  44. Proof by Exhaustion: "An issue or two of a journal devoted to your proof is useful."
  45. Proof by Omission: "The reader may easily supply the details."
  46. Proof by Obfuscation: "A long plotless sequence of true and/or meaningless syntactically related statements."
  47. Proof by Wishful Citation: "The author cites the negation, converse, or generalization of a theorem from the literature to support his claims."
  48. Proof by Funding: "How could three different government agencies by wrong?"
  49. Proof by Eminent Authority: "I saw Karp in the elevator and he said it was probably NP-complete."
  50. Proof by Personal Communication: "Eight-Dimensional colored cycle stripping is NP-complete [Karp, in a personal conversation.]"
  51. Proof by Reduction to the Wrong Problem: "To see that infinite-dimensional colored cycle stripping is decidable, we reduce it to the halting problem."
  52. 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."
  53. Proof by Importance: "A large body of useful consequences all follow from the proposition in question."
  54. Proof by Accumulated Evidence: "Long and diligent search has not revealed a counterexample."
  55. Proof by Cosmology: "The negation of the proposition is unimaginable or meaningless.  Popular for proofs of the existence of God."
  56. Proof by Mutual Reference: "In reference A, Theorem 5 is said to follow from Theorem 3 in reference B, which is show to follow from Corollary 6.2 in reference C, which is an easy consequence of Theorem 5 in reference A."
  57. Proof by Metaproof: "A method is given to construct the desired proof. The correctness of the method is proved by any of these techniques."
  58. Proof by Picture: "A more convincing form of proof by example.  Combines well with proof by omission."
  59. Proof by Vehement Assertion: "It is useful to have some kind of authority relation to the audience."
  60. Proof by Ghost Reference: "Nothing even remotely resembling the cited theorem appears in the reference given."
  61. Proof by Forward Reference: "Reference is usually to a forthcoming paper of the author, which is often not as forthcoming as at first."
  62. Proof by Semantic Shift: "Some of the standard but inconvenient definitions are changed for the statement of the result."
  63. Proof by Appeal to Intuition: "Cloud-shaped drawings frequently help here."

Adapted from: From Dick A. Wood in The Mathematics Teacher November 1998
and from Steve Phipps.  Also from Dana Angluin, Sigact News, Winter-Spring 1983, Volume 15 #1


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