Knuth's Generalization of McCarthy's 91 Function

Donald E. Knuth of Stanford University asks for a ``proof by computer'' of a theorem about his generalization, involving real numbers, of John McCarthy's 91 function. This talk explores a largely successful attempt to use the theorem prover ACL2 to meet Knuth's challenge. Real numbers are dealt with by mechanically verifying results that are true, not only about the field of all real numbers, but also about every subfield of that field.