--- /dev/null
+(* Copyright (C) 2000, HELM Team.
+ *
+ * This file is part of HELM, an Hypertextual, Electronic
+ * Library of Mathematics, developed at the Computer Science
+ * Department, University of Bologna, Italy.
+ *
+ * HELM is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * HELM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HELM; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ *
+ * For details, see the HELM World-Wide-Web page,
+ * http://cs.unibo.it/helm/.
+ *)
+
+type id = string (* identifier *)
+
+type qid = id * bool * id list (* qualified identifier: name, is local?, qualifiers *)
+
+type term = Sort of bool (* sorts: true = TYPE, false = PROP *)
+ | GRef of qid * term list (* reference: name, arguments *)
+ | Appl of term * term (* application: argument, function *)
+ | Abst of id * term * term (* abstraction: name, type, body *)
+
+type item = Section of id option (* section: Some = open/reopen, None = close last *)
+ | Context of qid option (* context: Some = last node, None = root *)
+ | Block of id * term (* block opener: name, type *)
+ | Decl of id * term (* declaration: name, type *)
+ | Def of id * term * bool * term (* definition: name, type, transparent?, body *)
+
+type book = item list (* book *)