A good introductory book on HOL (Higher Order Logic) is: Introduction to HOL: A theorem proving environment for higher order logic, edited by M.J.C. Gordon and T.F. Melham, 1993. ISBN 0-521-44189-7. Order from Amazon USA or Amazon UK. See also: * Publisher's information from Cambridge University Press. ISBN 0-521-44189-7. * A book review of An introduction to HOL by Graham Hutton.