* Pure/library.ML: several combinators for linear functional transformations;
* Pure/library.ML: canonical list combinators fold, fold_rev, and fold_yield;
* Pure/term.ML: combinators fold_atyps, fold_aterms, fold_term_types, fold_types;
use "../settings.ML";
no_document use_thy "While_Combinator";
use_thy "simp";
use_thy "WFrec";
use_thy "Partial";