Introduce some masked tgba.

* src/tgba/tgbamask.cc, src/tgba/tgbamask.hh,
src/tgba/tgbaproxy.cc, src/tgba/tgbaproxy.hh: New files.
* src/tgba/Makefile.am: Add them.
* src/tgbatest/explicit3.cc, src/tgbatest/explicit3.test:
New files.
* src/tgbatest/Makefile.am: Add them.

src/tgba/tgbaproxy.hh

@@ -0,0 +1,71 @@
+// Copyright (C) 2013 Laboratoire de Recherche et
+// Développement de l'Epita (LRDE).
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot 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 3 of the License, or
+// (at your option) any later version.
+//
+// Spot 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#ifndef SPOT_TGBA_TGBAPROXY_HH
+# define SPOT_TGBA_TGBAPROXY_HH
+
+#include "tgba.hh"
+
+namespace spot
+{
+  /// \ingroup tgba_on_the_fly_algorithms
+  /// \brief A TGBA proxy.
+  ///
+  /// This implements a simple proxy to an existing
+  /// TGBA, forwarding all methods to the original.
+  /// By itself this class is pointless: better use the
+  /// original automaton right away.  However it is useful
+  /// to inherit from this class and override some of its
+  /// methods to implement some on-the-fly algorithm.
+  class SPOT_API tgba_proxy: public tgba
+  {
+  protected:
+    tgba_proxy(const tgba* original);
+
+  public:
+    virtual ~tgba_proxy();
+
+    virtual state* get_init_state() const;
+
+    virtual tgba_succ_iterator*
+    succ_iter(const state* local_state,
+	      const state* global_state = 0,
+	      const tgba* global_automaton = 0) const;
+
+    virtual bdd_dict* get_dict() const;
+
+    virtual std::string format_state(const state* state) const;
+
+    virtual std::string
+    transition_annotation(const tgba_succ_iterator* t) const;
+
+    virtual state* project_state(const state* s, const tgba* t) const;
+
+    virtual bdd all_acceptance_conditions() const;
+
+    virtual bdd neg_acceptance_conditions() const;
+
+  protected:
+    virtual bdd compute_support_conditions(const state* state) const;
+    virtual bdd compute_support_variables(const state* state) const;
+
+    const tgba* original_;
+  };
+}
+
+#endif // SPOT_TGBA_TGBA_HH