"{x. P x & x=t & Q x}" is now rewritten to "if P t & Q t then {t} else {}"
by the new simproc defColl_regroup. More precisely, the simproc pulls an
equation x=t (or t=x) out of a nest of conjunctions to the front where the
simp rule singleton_conj_conv(2) converts to "if".
use "../settings.ML";
use_thy "Tree";
use_thy "Tree2";
use_thy "Plus";
use_thy "case_exprs";
use_thy "fakenat";
use_thy "natsum";
use_thy "pairs";
use_thy "Option2";
use_thy "types";
use_thy "prime_def";
use_thy "simp";
use_thy "Itrev";
use_thy "AdvancedInd";
use_thy "appendix";