from: http://plms.oxfordjournals.org/cgi/reprint/s2-42/1/230
originally published in:
A. M. Turing
On Computable Numbers, with an Application to the Entscheidungsproblem
Proc. London Math. Soc. 1937 s2-42: 230-265; doi:10.1112/plms/s2-42.1.230
Turing_OnComputableNumbers_1936