dest_ctyp: raise exception for non-constructor;
dest_comb: replaced expensive fastype_of by Term.argument_type;
dest_abs: replaced expensive variant_abs by Term.dest_abs;
hyps: fast_term_ord;
use "../settings.ML";
no_document use_thy "While_Combinator";
use_thy "simp";
use_thy "WFrec";
use_thy "Partial";