I was first exposed to the 2#2 problem in 1967 as a high school student working at the National Bureau of Standards. Afterwards I worked on it from time to time. Out of curiosity and frustration I gradually became a historian of the problem, accumulating a collection of papers about it. This survey is a happy consequence. I obtained a Ph.D. (1974) in analytic number theory at M.I.T. under the supervision of Harold Stark. I have been on the staff of AT&T Bell Laboratories since then, and have held visiting positions at the University of Maryland (mathematics) and Rutgers University (computer science). My research interests include computational complexity theory, number theory, and cryptography.

Conway's proof used Minsky machines, which have the same computational power as Turing machines.