simplified/refined document model: collection of named nodes, without proper dependencies yet;
moved basic type definitions for ids and edits from Isar_Document to Document;
removed begin_document/end_document for now -- nodes emerge via edits;
edits refer to named nodes explicitly;
(* ID: $Id$ *)
use_thy "Examples";
use_thy "Functions";
use_thy "Relations";
use_thy "Recur";