Cogprints: No conditions. Results ordered Title. 2018-01-17T14:22:19ZEPrintshttp://cogprints.org/images/sitelogo.gifhttp://cogprints.org/1998-02-27Z2011-03-11T08:53:53Zhttp://cogprints.org/id/eprint/414This item is in the repository with the URL: http://cogprints.org/id/eprint/4141998-02-27ZA Tough Nut for Proof ProceduresIt is well known to be impossible to tile with dominoes a checkerboard with two opposite corners deleted. This fact is readily stated in the first order predicate calculus, but the usual proof which involves a parity and counting argument does not readily translate into predicate calculus. We conjecture that this problem will be very difficult for programmed proof procedures,.John McCarthy