Doxygen comments.

* src/ta/ta.cc, src/ta/ta.hh, src/ta/taexplicit.hh,
src/ta/taproduct.cc, src/ta/taproduct.hh, src/ta/tgbtaexplicit.cc,
src/ta/taexplicit.cc, src/ta/tgbtaproduct.cc,
src/taalgos/emptinessta.cc, src/taalgos/emptinessta.hh,
src/taalgos/tgba2ta.cc, src/taalgos/tgba2ta.hh,
src/tgbatest/ltl2ta.test, src/tgbatest/ltl2tgba.cc: Add Doxygen
comments.

src/ta/taexplicit.hh

@@ -37,7 +37,8 @@ namespace spot
   class ta_explicit_succ_iterator;
   class ta_explicit;
 
-  /// ta_explicit explicit representa_explicittion of a Testing Automata_explicit
+  /// Explicit representation of a spot::ta.
+  /// \ingroup ta_representation
   class ta_explicit : public ta
   {
   public:
@@ -53,7 +54,6 @@ namespace spot
     void
     add_to_initial_states_set(state* s, bdd condition = bddfalse);
 
-
     void
     create_transition(state_ta_explicit* source, bdd condition,
         bdd acceptance_conditions, state_ta_explicit* dest,
@@ -145,11 +145,12 @@ namespace spot
   };
 
   /// states used by spot::ta_explicit.
-  /// \ingroup ta_
+  /// \ingroup ta_representation
   class state_ta_explicit : public spot::state
   {
   public:
 
+    /// Explicit transitions.
     struct transition
     {
       bdd condition;
@@ -176,11 +177,11 @@ namespace spot
     virtual state_ta_explicit*
     clone() const;
 
-    virtual void destroy() const
+    virtual void
+    destroy() const
     {
     }
 
-
     virtual
     ~state_ta_explicit()
     {
@@ -214,9 +215,12 @@ namespace spot
     void
     set_initial_state(bool is_initial_state);
 
+    /// \brief Return true if the state has no successors
     bool
     is_hole_state() const;
 
+    /// \brief Remove stuttering transitions
+    /// and transitions leading to states having no successors
     void
     delete_stuttering_and_hole_successors();
 
@@ -257,9 +261,6 @@ namespace spot
     virtual bdd
     current_acceptance_conditions() const;
 
-    virtual bool
-    is_stuttering_transition() const;
-
   private:
     state_ta_explicit::transitions* transitions_;
     state_ta_explicit::transitions::const_iterator i_;