floor and ceiling definitions are not code equations -- this enables trivial evaluation of floor and ceiling
Identifiers of some old CVS file versions
=========================================
src/Pure/General/file.ML 1.18 6cdd6a8da9b9
src/Pure/thm.ML 1.189 4b339d3907a0 (referenced in 25f28f9c28a3 as "2005-01-24 (revision 1.44)")
src/Pure/type.ML 1.65 0d984ee030a1