1. John J. O'Conner and Edmund F. Robertson. "Alonzo Church" in The MacTutor History of Mathematics Archive   (University of St. Andrews Scotland, School of Mathematics and Statistics, http://turnbull.dcs.st-and.ac.uk/history/Mathematicians/Church.html, 2003 September 13, archived for reference http://www.dgatx.com/computing/people/John-OConner/pubs/2003/Alonzo-Church/Church.html, 2003 September 13)