Emil L. Post (1897 – 1954)

Post was mathematician and logician who’s area of work became known as “computational theory”. In the 1920ies he had conjectured about a certain kind of logical system. Even he never officially published anything this “Post’s-Machine” preceded the proof provided later by Turing, Church and Gödel.

When Gödel published his Incompleteness Theorems in 1931, Post realised that he had waited too long to publish what he had proved and that now the whole credit would go to Gödel. In a postcard written to Gödel in 1938, just after they had met for the first time, Post wrote:-

… for fifteen years I carried around the thought of astounding the mathematical world with my unorthodox ideas, and meeting the man chiefly responsible for the vanishing of that dream rather carried me away. Since you seemed interested in my way of arriving at these new developments perhaps Church can show you a long letter I wrote to him about them. As for any claims I might make perhaps the best I can say is that I would have proved Gödel’s Theorem in 1921 – had I been Gödel.

He is also know for his Post-canonical system which is a formalism for modelling logical theories which are Turing-complete. They can be seen as the first approach to string-rewriting and regular expressions.

Sad facts:

  • As a child Post had lost an arm during an accident.
  • He suffered all his adult life from crippling manic-depressive disease at a time when no drug therapy was available for this malady.
  • Post died from a heart attack at the age of 57 as a direct consequence of the electric shock treatment he received for his mental illness.
  • Even though his work proofs and precedes what was later established by Church, Gödel & Turing, his contribution is hardly ever mentioned.


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