misc tuning: more concise operations on prems (without change of exceptions);
discontinue odd clone Drule.cprems_of (see also 991a3feaf270);
@article{church40,
author = "Alonzo Church",
title = "A Formulation of the Simple Theory of Types",
journal = "Journal of Symbolic Logic",
year = 1940,
volume = 5,
pages = "56-68"}
@TechReport{Gordon:1985:HOL,
author = {M. J. C. Gordon},
title = {{HOL}: A machine oriented formulation of higher order logic},
institution = {University of Cambridge Computer Laboratory},
year = 1985,
number = 68
}