Some reflections on Alan Turing's centenary (Q1943938)

Summary: We review two of \textit{Alan Turing}'s chief publications in mathematical logic: the classic paper [``On computable numbers'', Proc. Lond. Math. Soc., II. Ser. 42, 230--265 (1936; Zbl 0016.09701)] and the less well-known paper [``Systems of logic based on ordinals'', ibid. 45, 161--228 (1939; Zbl 0021.09704)]. Whilst the former has rightly received enormous attention the latter is really only known amongst logicians. We outline some of the history and background to the first, whilst emphasising a viewpoint often forgotten in discussions of the so-called `Church-Turing thesis'; we sketch the development of the second paper and see why its results were equivocal and perhaps somewhat disappointing to Turing.