2009-10-17 wenzelm 2009-10-17 eliminated hard tabulators, guessing at each author's individual tab-width; tuned headers;
2009-07-23 wenzelm 2009-07-23 renamed simpset_of to global_simpset_of, and local_simpset_of to simpset_of -- same for claset and clasimpset;
2008-02-11 krauss 2008-02-11 Made theory names in ZF disjoint from HOL theory names to allow loading both developments in a single session (but not merge them).