* src/ltlvisit/clone.hh, src/ltlvisit/clone.cc: New files.

* src/ltlvisit/Makefile.am (libltlvisit_a_SOURCES): Add them.
* src/ltlvisit/lunabbrev.hh, src/ltlvisit/lunabbrev.cc: Inherit
from clone_visitor and remove all useless methods (now inherited).

src/ltlvisit/clone.hh

@@ -0,0 +1,37 @@
+#ifndef SPOT_LTLVISIT_CLONE_HH
+# define SPOT_LTLVISIT_CLONE_HH
+
+#include "ltlast/formula.hh"
+#include "ltlast/visitor.hh"
+
+namespace spot 
+{
+  namespace ltl
+  {
+    // This visitor is public, because it's convenient
+    // to derive from it and override part of its methods.
+    class clone_visitor : public const_visitor
+    {
+    public:
+      clone_visitor();
+      virtual ~clone_visitor();
+
+      formula* result() const;
+      
+      void visit(const atomic_prop* ap);
+      void visit(const unop* uo);
+      void visit(const binop* bo);
+      void visit(const multop* mo);
+      void visit(const constant* c);
+	
+      virtual formula* recurse(const formula* f);
+      
+    protected:
+      formula* result_;
+    };
+
+    formula* clone(const formula* f);
+  }
+}
+
+#endif // SPOT_LTLVISIT_LUNABBREV_HH