“However, in all honesty, I must say that one must essentially forget that all proofs are transcribed in this formal language. In order to think productively, one must use all the intuitive and informal methods of reasoning at one's disposal. At the very end one must check that no errors have been committed; but in practice set theory is treated as any other branch of mathematics. The reason that we can do this is that we will never speak about proofs but only about models.”

— Paul Cohen

p. 1078 of "The discovery of forcing." http://www.logic.univie.ac.at/~ykhomski/ST2013/The%20Discovery%20of%20Forcing.pdf Rocky Mountain Journal of Mathematics 32, no. 4 (2002): 1071–1100.

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Paul Cohen 5

American mathematician 1934–2007

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