diff --git a/src/ltlvisit/length.cc b/src/ltlvisit/length.cc
new file mode 100644
index 000000000..882431889
--- /dev/null
+++ b/src/ltlvisit/length.cc
@@ -0,0 +1,96 @@
+// Copyright (C) 2004  Laboratoire d'Informatique de Paris 6 (LIP6),
+// département Systèmes Répartis Coopératifs (SRC), Université Pierre
+// et Marie Curie.
+//
+// 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 2 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 Spot; see the file COPYING.  If not, write to the Free
+// Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+// 02111-1307, USA.
+
+#include "length.hh"
+#include "ltlast/allnodes.hh"
+#include "ltlast/visitor.hh"
+
+namespace spot
+{
+  namespace ltl
+  {
+
+   class length_visitor : public const_visitor
+    {
+    public:
+
+      length_visitor()
+      {
+	result_ = 0;
+      }
+
+      virtual
+      ~length_visitor()
+      {
+      }
+
+      int
+      result() const
+      {
+	return result_;
+      }
+
+      void
+      visit(const atomic_prop*)
+      {
+	result_ = 1;
+      }
+
+      void
+      visit(const constant*)
+      {
+	result_ = 1;
+      }
+
+      void
+      visit(const unop* uo)
+      {
+	result_ = 1 + length(uo->child());
+      }
+
+      void
+      visit(const binop* bo)
+      {
+	result_ = 1 + length(bo->first()) + length(bo->second());
+      }
+
+      void
+      visit(const multop* mo)
+      {
+	unsigned mos = mo->size();
+	for (unsigned i = 0; i < mos; ++i)
+	  result_ += length(mo->nth(i));
+      }
+
+    protected:
+      int result_; // size of the formula
+    };
+
+    int
+    length(const formula* f)
+    {
+      length_visitor v;
+      const_cast<formula*>(f)->accept(v);
+      return v.result();
+    }
+
+  }
+}