directions. He atomised the Turing 5-tuples into 4-tuples--motion instructions separate from print/erase instructions. Although his 1936 model is ambiguous about this, Post's 1947 model did not require sequential instruction execution.

His extremely simple model can emulate any Turing machine, and although his 1936 Formulation 1 does not use the word "program" or "machine", it is effectively a formulation of a very primitive programmable computer and associated programming language, with the