--- /dev/null
+<?xml encoding="ISO-8859-1"?>
+
+<!-- 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/. -->
+
+<!-- DTD for backward pointers metadata. For every object, it lists -->
+<!-- all the other objects directly depending on it. -->
+
+<!ELEMENT rdf:RDF (h:Object)>
+<!ATTLIST rdf:RDF
+ xml:lang CDATA #REQUIRED
+ xmlns:rdf CDATA #FIXED "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+ xmlns:h CDATA #FIXED "http://www.cs.unibo.it/helm/schemas/mattone.rdf#">
+
+<!ELEMENT h:Object (h:backPointer)*>
+<!ATTLIST h:Object
+ rdf:about CDATA #REQUIRED>
+
+<!ELEMENT h:backPointer (h:Occurrence)>
+
+<!ELEMENT h:Occurrence (h:position,h:occurrence)>
+
+<!-- Either MainHypothesis or InHypothesis or InConclusion or -->
+<!-- MainConclusion or InBody. -->
+<!ELEMENT h:position (#PCDATA)>
+
+<!ELEMENT h:occurrence (#PCDATA)>
--- /dev/null
+<?xml encoding="ISO-8859-1"?>
+
+<!-- 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/. -->
+
+<!-- DTD for forward pointers metadata. For every object, it lists -->
+<!-- all the other objects it depends on. -->
+
+<!ELEMENT rdf:RDF (h:Object)>
+<!ATTLIST rdf:RDF
+ xml:lang CDATA #REQUIRED
+ xmlns:rdf CDATA #FIXED "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+ xmlns:h CDATA #FIXED "http://www.cs.unibo.it/helm/schemas/mattone.rdf#">
+
+<!ELEMENT h:Object (h:refObj)*>
+<!ATTLIST h:Object
+ rdf:about CDATA #REQUIRED>
+
+<!ELEMENT h:refObj (h:Occurrence)>
+
+<!ELEMENT h:Occurrence (h:position,h:occurrence)>
+
+<!-- Either MainHypothesis or InHypothesis or InConclusion or -->
+<!-- MainConclusion or InBody. -->
+<!ELEMENT h:position (#PCDATA)>
+
+<!ELEMENT h:occurrence (#PCDATA)>