diff --git a/src/ta/tgtaexplicit.cc b/src/ta/tgtaexplicit.cc
index 102b7aaac..1cf68c211 100644
--- a/src/ta/tgtaexplicit.cc
+++ b/src/ta/tgtaexplicit.cc
@@ -33,66 +33,67 @@ namespace spot
   tgta_explicit::tgta_explicit(const tgba* tgba, bdd all_acceptance_conditions,
 			       state_ta_explicit* artificial_initial_state,
 			       bool own_tgba) :
-    ta_explicit(tgba, all_acceptance_conditions, artificial_initial_state, own_tgba)
+    ta_(tgba, all_acceptance_conditions, artificial_initial_state, own_tgba)
   {
   }
 
   state*
   tgta_explicit::get_init_state() const
   {
-    return ta_explicit::get_artificial_initial_state();
+    return ta_.get_artificial_initial_state();
   }
 
   tgba_succ_iterator*
   tgta_explicit::succ_iter(const spot::state* state, const spot::state*,
-      const tgba*) const
+			   const tgba*) const
   {
-    return ta_explicit::succ_iter(state);
+    return ta_.succ_iter(state);
   }
 
   bdd
   tgta_explicit::compute_support_conditions(const spot::state* in) const
   {
-    return get_tgba()->support_conditions(
-        ((const state_ta_explicit*) in)->get_tgba_state());
+    const state_ta_explicit* s = down_cast<const state_ta_explicit*>(in);
+    assert(s);
+    return ta_.get_tgba()->support_conditions(s->get_tgba_state());
   }
 
   bdd
   tgta_explicit::compute_support_variables(const spot::state* in) const
   {
-    return get_tgba()->support_variables(
-        ((const state_ta_explicit*) in)->get_tgba_state());
+    const state_ta_explicit* s = down_cast<const state_ta_explicit*>(in);
+    assert(s);
+    return ta_.get_tgba()->support_variables(s->get_tgba_state());
   }
 
   bdd_dict*
   tgta_explicit::get_dict() const
   {
-    return ta_explicit::get_dict();
+    return ta_.get_dict();
   }
 
   bdd
   tgta_explicit::all_acceptance_conditions() const
   {
-
-    return ta_explicit::all_acceptance_conditions();
+    return ta_.all_acceptance_conditions();
   }
 
   bdd
   tgta_explicit::neg_acceptance_conditions() const
   {
-    return get_tgba()->neg_acceptance_conditions();
+    return ta_.get_tgba()->neg_acceptance_conditions();
   }
 
   std::string
   tgta_explicit::format_state(const spot::state* s) const
   {
-    return ta_explicit::format_state(s);
+    return ta_.format_state(s);
   }
 
   spot::tgba_succ_iterator*
   tgta_explicit::succ_iter_by_changeset(const spot::state* s, bdd chngset) const
   {
-    return ta_explicit::succ_iter(s, chngset);
+    return ta_.succ_iter(s, chngset);
   }
 
 }
diff --git a/src/ta/tgtaexplicit.hh b/src/ta/tgtaexplicit.hh
index 86a9a5f6b..39ed46230 100644
--- a/src/ta/tgtaexplicit.hh
+++ b/src/ta/tgtaexplicit.hh
@@ -36,7 +36,7 @@ namespace spot
 
   /// Explicit representation of a spot::tgta.
   /// \ingroup ta_representation
-  class tgta_explicit : public tgta, public ta_explicit
+  class tgta_explicit : public tgta
   {
   public:
     tgta_explicit(const tgba* tgba, bdd all_acceptance_conditions,
@@ -44,30 +44,30 @@ namespace spot
 		  bool own_tgba = false);
 
     // tgba interface
-    virtual spot::state*
-    get_init_state() const;
+    virtual spot::state* get_init_state() const;
+
     virtual tgba_succ_iterator*
     succ_iter(const spot::state* local_state, const spot::state* global_state =
         0, const tgba* global_automaton = 0) const;
+
     virtual bdd_dict*
     get_dict() const;
 
-    virtual bdd
-    all_acceptance_conditions() const;
-    virtual bdd
-    neg_acceptance_conditions() const;
+    const ta_explicit* get_ta() const { return &ta_; }
+    ta_explicit* get_ta() { return &ta_; }
 
-    virtual std::string
-    format_state(const spot::state* s) const;
+    virtual bdd all_acceptance_conditions() const;
+    virtual bdd neg_acceptance_conditions() const;
+
+    virtual std::string format_state(const spot::state* s) const;
 
     virtual tgba_succ_iterator*
     succ_iter_by_changeset(const spot::state* s, bdd change_set) const;
   protected:
-    virtual bdd
-    compute_support_conditions(const spot::state* state) const;
-    virtual bdd
-    compute_support_variables(const spot::state* state) const;
+    virtual bdd compute_support_conditions(const spot::state* state) const;
+    virtual bdd compute_support_variables(const spot::state* state) const;
 
+    ta_explicit ta_;
   };
 
 }
diff --git a/src/taalgos/minimize.cc b/src/taalgos/minimize.cc
index 7de54cf76..83eaba3f8 100644
--- a/src/taalgos/minimize.cc
+++ b/src/taalgos/minimize.cc
@@ -514,13 +514,12 @@ namespace spot
     std::list<hash_set*>::iterator itdone;
     for (itdone = partition.begin(); itdone != partition.end(); ++itdone)
       delete *itdone;
-    //delete ta_;
 
     return res;
   }
 
-  tgta*
-  minimize_tgta(const tgta* tgta_)
+  tgta_explicit*
+  minimize_tgta(const tgta_explicit* tgta_)
   {
 
     tgba_explicit_number* tgba = new tgba_explicit_number(tgta_->get_dict());
@@ -528,19 +527,17 @@ namespace spot
     tgta_explicit* res = new tgta_explicit(tgba, tgta_->all_acceptance_conditions(),
 					   0, /* own_tgba = */ true);
 
-    //TODO copier le tgta_ dans un tgta_explicit au lieu de faire un cast...
-    const ta_explicit* tgta = dynamic_cast<const tgta_explicit*> (tgta_);
+    const ta_explicit* ta = tgta_->get_ta();
 
-    partition_t partition = build_partition(tgta);
+    partition_t partition = build_partition(ta);
 
     // Build the minimal tgta automaton.
-    build_result(tgta, partition, tgba, res);
+    build_result(ta, partition, tgba, res->get_ta());
 
     // Free all the allocated memory.
     std::list<hash_set*>::iterator itdone;
     for (itdone = partition.begin(); itdone != partition.end(); ++itdone)
       delete *itdone;
-    //delete ta_;
 
     return res;
   }
diff --git a/src/taalgos/minimize.hh b/src/taalgos/minimize.hh
index 793db96cd..a4c68a912 100644
--- a/src/taalgos/minimize.hh
+++ b/src/taalgos/minimize.hh
@@ -1,5 +1,6 @@
-// Copyright (C) 2009, 2010, 2011 Laboratoire de Recherche et Développement
-// de l'Epita (LRDE).
+// -*- coding: utf-8 -*-
+// Copyright (C) 2009, 2010, 2011, 2012 Laboratoire de Recherche et
+// DĂ©veloppement de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
 //
@@ -23,7 +24,7 @@
 
 # include "ta/ta.hh"
 # include "ta/tgta.hh"
-# include "ta/taexplicit.hh"
+# include "ta/tgtaexplicit.hh"
 
 namespace spot
 {
@@ -71,8 +72,8 @@ namespace spot
   /// the acceptance conditions of the outgoing transitions.
   ///
   /// \param tgta_ the TGTA automaton to convert into a simplified TGTA
-  tgta*
-  minimize_tgta(const tgta* tgta_);
+  tgta_explicit*
+  minimize_tgta(const tgta_explicit* tgta_);
 
 /// @}
 }
diff --git a/src/taalgos/tgba2ta.cc b/src/taalgos/tgba2ta.cc
index 847b0c2b3..4a8ff3d1e 100644
--- a/src/taalgos/tgba2ta.cc
+++ b/src/taalgos/tgba2ta.cc
@@ -621,28 +621,30 @@ compute_livelock_acceptance_states(ta_explicit* testing_automata,
 
     // build a Generalized TA automaton involving a single_pass_emptiness_check
     // (without an artificial livelock state):
-    build_ta(tgta, atomic_propositions_set_, false, true, false);
+    ta_explicit* ta = tgta->get_ta();
+    build_ta(ta, atomic_propositions_set_, false, true, false);
 
-    trace
-      << "***tgba_to_tgbta: POST build_ta***" << std::endl;
+    trace << "***tgba_to_tgbta: POST build_ta***" << std::endl;
 
     // adapt a ta automata to build tgta automata :
-    ta::states_set_t states_set = tgta->get_states_set();
+    ta::states_set_t states_set = ta->get_states_set();
     ta::states_set_t::iterator it;
-    tgba_succ_iterator* initial_states_iter = tgta->succ_iter(
-        tgta->get_artificial_initial_state());
+    tgba_succ_iterator* initial_states_iter =
+      ta->succ_iter(ta->get_artificial_initial_state());
     initial_states_iter->first();
     if (initial_states_iter->done())
-      return tgta;
-    bdd first_state_condition = (initial_states_iter)->current_condition();
+      {
+	delete initial_states_iter;
+	return tgta;
+      }
+    bdd first_state_condition = initial_states_iter->current_condition();
     delete initial_states_iter;
 
     bdd bdd_stutering_transition = bdd_setxor(first_state_condition,
-        first_state_condition);
+					      first_state_condition);
 
     for (it = states_set.begin(); it != states_set.end(); it++)
       {
-
         state_ta_explicit* state = static_cast<state_ta_explicit*> (*it);
 
         state_ta_explicit::transitions* trans = state->get_transitions();
@@ -652,21 +654,18 @@ compute_livelock_acceptance_states(ta_explicit* testing_automata,
             bool trans_empty = (trans == 0 || trans->empty());
             if (trans_empty || state->is_accepting_state())
               {
-                tgta->create_transition(state, bdd_stutering_transition,
-                    tgta->all_acceptance_conditions(), state);
+                ta->create_transition(state, bdd_stutering_transition,
+                    ta->all_acceptance_conditions(), state);
               }
 
           }
 
-        if (state->compare(tgta->get_artificial_initial_state()))
-          tgta->create_transition(state, bdd_stutering_transition, bddfalse,
-              state);
+        if (state->compare(ta->get_artificial_initial_state()))
+          ta->create_transition(state, bdd_stutering_transition, bddfalse, state);
 
         state->set_livelock_accepting_state(false);
         state->set_accepting_state(false);
-        trace
-          << "***tgba_to_tgbta: POST create_transition ***" << std::endl;
-
+        trace << "***tgba_to_tgbta: POST create_transition ***" << std::endl;
       }
 
     return tgta;
diff --git a/src/tgbatest/ltl2tgba.cc b/src/tgbatest/ltl2tgba.cc
index 5ac0de8dc..4858fe514 100644
--- a/src/tgbatest/ltl2tgba.cc
+++ b/src/tgbatest/ltl2tgba.cc
@@ -1153,7 +1153,7 @@ main(int argc, char** argv)
             }
           if (tgta_opt)
             {
-              spot::tgta* tgta = tgba_to_tgta(a, atomic_props_set_bdd);
+              spot::tgta_explicit* tgta = tgba_to_tgta(a, atomic_props_set_bdd);
               if (opt_bisim_ta)
                 {
 		  tm.start("TA bisimulation");
diff --git a/wrap/python/ajax/spot.in b/wrap/python/ajax/spot.in
index fd0b7b872..6588f2aa1 100755
--- a/wrap/python/ajax/spot.in
+++ b/wrap/python/ajax/spot.in
@@ -289,8 +289,8 @@ def render_automaton(automaton, dont_run_dot, issba, deco = None):
     dotsrc = spot.ostringstream()
     if isinstance(automaton, spot.ta): # TA/GTA
         spot.dotty_reachable(dotsrc, automaton)
-    elif hasattr(automaton, 'as_ta'): # TGTA
-        spot.dotty_reachable(dotsrc, automaton.as_ta())
+    elif hasattr(automaton, 'get_ta'): # TGTA
+        spot.dotty_reachable(dotsrc, automaton.get_ta())
     else:                       # TGBA
         spot.dotty_reachable(dotsrc, automaton, issba, deco)
     render_dot_maybe(dotsrc.str(), dont_run_dot)
diff --git a/wrap/python/spot.i b/wrap/python/spot.i
index 961f63132..83a9b6cc4 100644
--- a/wrap/python/spot.i
+++ b/wrap/python/spot.i
@@ -317,14 +317,6 @@ using namespace spot;
 
 }
 
-%extend spot::tgta_explicit {
-  const spot::ta*
-  as_ta(const spot::tgta_explicit* t)
-  {
-    return dynamic_cast<const spot::ta*>(t);
-  }
-}
-
 %nodefaultctor std::ostream;
 namespace std {
   class ostream {};