How to Write a Proof (1993)

by Leslie Lamport.

A method of writing proofs is proposed that makes it much harder to prove things that are not true. The method, based on hierarchical structuring, is simple and practical ... Mathematical notation has improved over the past few centuries. In the seventeenth century, a mathematician might have written There do not exist four positive integers, the last being greater than two, such that the sum of the first two, each raised to the power of the fourth, equals the third raised to that same power. [via]

http://research.microsoft.com/users/lamport/p...