POST, Emil Leon (1897-1954). 'Formal Reductions of the General Combinatorial Decision Problem.' Offprint from: American Journal of Mathematics, Vol. LXV, No. 2, April 1943. 8° (242 x 162mm). 20pp., 197-215, [1, blank]. Original buff wrappers, stapled (tiny spot to upper wrapper and first leaf, staples rusted, faint soiling). Provenance: ALAN TURING (two manuscript corrections to pp.204-205 possibly in Turing's hand; bequeathed to:) -- R.O. Gandy (no sign of provenance).

ALAN TURING'S COPY OF THE SECOND OF POST'S IMPORTANT PAPERS OUTLINING HIS APPROACH TO UNDECIDABLE PROBLEMS. Post’s original approach historically preceded that of Gödel, Church and Turing, but he did not follow it through far enough until 1936 when he published his first paper on undecidable problems in general formal systems. As a result he was recognised as one of the great originators of this field. In this second paper, Post describes the reduction of the decision problem for the complicated canonical form to that for the simple normal form, usually referred to as his 'normal form theorem'. A VERY RARE OFFPRINT WITH EXCEPTIONAL PROVENANCE.

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