diff --git a/NEWS b/NEWS
index 0fe750ac4..0f5da75fa 100644
--- a/NEWS
+++ b/NEWS
@@ -140,7 +140,7 @@ New in spot 2.7.5.dev (not yet released)
     properties.  This can be altered with the SPOT_PR_CHECK
     environment variable.
 
-  Backward incompatibilities:
+  Deprecation notices:
 
   - The virtual function twa::intersecting_run() no longuer takes a
     second "from_other" Boolean argument.  This is a backward
@@ -149,6 +149,11 @@ New in spot 2.7.5.dev (not yet released)
     call this function with two argument, a non-virtual version of the
     function has been introduced and marked as deprecated.
 
+  - The spot::acc_cond::format() methods have been deprecated.  These
+    were used to display acceptance marks, but acceptance marks are
+    unrelated to acceptance conditions, so it's better to simply print
+    marks with operator<< without this extra step.
+
   Bugs fixed:
 
   - The gf_guarantee_to_ba() is relying on an inplace algorithm that
diff --git a/spot/priv/satcommon.cc b/spot/priv/satcommon.cc
index 53f9a81cc..21d75eee1 100644
--- a/spot/priv/satcommon.cc
+++ b/spot/priv/satcommon.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2013-2018 Laboratoire de Recherche et Développement
+// Copyright (C) 2013-2019 Laboratoire de Recherche et Développement
 // de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -97,7 +97,7 @@ namespace spot
 
   std::string
   vars_helper::format_t(bdd_dict_ptr& debug_dict, unsigned src, bdd& cond,
-      unsigned dst)
+                        unsigned dst)
   {
     std::ostringstream buffer;
     buffer << '<' << src << ',' << bdd_format_formula(debug_dict, cond)
@@ -107,31 +107,30 @@ namespace spot
 
   std::string
   vars_helper::format_ta(bdd_dict_ptr& debug_dict,
-      const acc_cond* debug_cand_acc, unsigned src, bdd& cond, unsigned dst,
-      const acc_cond::mark_t& acc)
+                         unsigned src, bdd& cond, unsigned dst,
+                         const acc_cond::mark_t& acc)
   {
     std::ostringstream buffer;
     buffer << '<' << src << ',' << bdd_format_formula(debug_dict, cond)
-      << ',' << debug_cand_acc->format(acc) << ',' << dst << '>';
+           << ',' << acc << ',' << dst << '>';
     return buffer.str();
   }
 
   std::string
-  vars_helper::format_p(const acc_cond* debug_cand_acc,
-      const acc_cond* debug_ref_acc, unsigned src_cand, unsigned src_ref,
-      unsigned dst_cand, unsigned dst_ref, acc_cond::mark_t acc_cand,
-      acc_cond::mark_t acc_ref)
+  vars_helper::format_p(unsigned src_cand, unsigned src_ref,
+                        unsigned dst_cand, unsigned dst_ref,
+                        acc_cond::mark_t acc_cand, acc_cond::mark_t acc_ref)
   {
     std::ostringstream buffer;
     buffer << '<' << src_cand << ',' << src_ref << ',' << dst_cand << ','
-      << dst_ref << ", " << debug_cand_acc->format(acc_cand) << ", "
-      << debug_ref_acc->format(acc_ref) << '>';
+           << dst_ref << ", " << acc_cand << ", "
+           << acc_ref << '>';
     return buffer.str();
   }
 
   std::string
   vars_helper::format_p(unsigned src_cand, unsigned src_ref, unsigned dst_cand,
-      unsigned dst_ref)
+                        unsigned dst_ref)
   {
     std::ostringstream buffer;
     buffer << '<' << src_cand << ',' << src_ref;
diff --git a/spot/priv/satcommon.hh b/spot/priv/satcommon.hh
index a8403bff7..653212a92 100644
--- a/spot/priv/satcommon.hh
+++ b/spot/priv/satcommon.hh
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2013-2016, 2018 Laboratoire de Recherche et
+// Copyright (C) 2013-2016, 2018, 2019 Laboratoire de Recherche et
 // Développement de l'Epita.
 //
 // This file is part of Spot, a model checking library.
@@ -207,24 +207,24 @@ public:
     /// \brief Use this function to get a string representation of a transition.
     std::string
     format_t(bdd_dict_ptr& debug_dict, unsigned src, bdd& cond,
-        unsigned dst);
+             unsigned dst);
 
     /// \brief Use this function to get a string representation of a transition
     /// acc.
     std::string
-    format_ta(bdd_dict_ptr& debug_dict, const acc_cond* debug_cand_acc,
-        unsigned src, bdd& cond, unsigned dst, const acc_cond::mark_t& acc);
+    format_ta(bdd_dict_ptr& debug_dict, unsigned src, bdd& cond, unsigned dst,
+              const acc_cond::mark_t& acc);
 
     /// \brief Use this function to get a string representation of a path var.
     std::string
-    format_p(const acc_cond* debug_cand_acc, const acc_cond* debug_ref_acc,
-        unsigned src_cand, unsigned src_ref, unsigned dst_cand,
-        unsigned dst_ref, acc_cond::mark_t acc_cand, acc_cond::mark_t acc_ref);
+    format_p(unsigned src_cand, unsigned src_ref,
+             unsigned dst_cand, unsigned dst_ref,
+             acc_cond::mark_t acc_cand, acc_cond::mark_t acc_ref);
 
     /// \brief Use this function to get a string representation of a path var.
     std::string
-    format_p(unsigned src_cand, unsigned src_ref, unsigned dst_cand,
-        unsigned dst_ref);
+    format_p(unsigned src_cand, unsigned src_ref,
+             unsigned dst_cand, unsigned dst_ref);
   };
 
   /// \brief Give a filename to save the log of the SAT minimization.
diff --git a/spot/taalgos/dot.cc b/spot/taalgos/dot.cc
index 91b6065a9..ba0f3d517 100644
--- a/spot/taalgos/dot.cc
+++ b/spot/taalgos/dot.cc
@@ -1,6 +1,7 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2010, 2012, 2014-2016, 2018 Laboratoire de Recherche
-// et Developpement de l Epita (LRDE).
+
+// Copyright (C) 2010, 2012, 2014-2016, 2018-2019 Laboratoire de
+// Recherche et Developpement de l Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
 //
@@ -239,8 +240,7 @@ namespace spot
         if (!opt_hide_sets_)
           {
             label += "\n";
-            label += t_automata_->acc().
-              format(si->acc());
+            label += si->acc().as_string();
           }
 
         os_ << "  " << in << " -> " << out << " [label=\"";
diff --git a/spot/twa/acc.hh b/spot/twa/acc.hh
index 05747a29e..cad84f7da 100644
--- a/spot/twa/acc.hh
+++ b/spot/twa/acc.hh
@@ -406,6 +406,13 @@ namespace spot
 
       SPOT_API
       friend std::ostream& operator<<(std::ostream& os, mark_t m);
+
+      std::string as_string() const
+      {
+        std::ostringstream os;
+        os << *this;
+        return os.str();
+      }
     };
 
     /// \brief Operators for acceptance formulas.
@@ -1842,20 +1849,22 @@ namespace spot
     /// that the condition is satisfied.
     mark_t accepting_sets(mark_t inf) const;
 
-    // FIXME: deprecate?
+    // Deprecated since Spot 2.8
+    SPOT_DEPRECATED("Use operator<< instead.")
     std::ostream& format(std::ostream& os, mark_t m) const
     {
-      auto a = m; // ???
-      if (!a)
+      if (!m)
         return os;
       return os << m;
     }
 
-    // FIXME: deprecate?
+    // Deprecated since Spot 2.8
+    SPOT_DEPRECATED("Use operator<< or mark_t::as_string() instead.")
     std::string format(mark_t m) const
     {
       std::ostringstream os;
-      format(os, m);
+      if (m)
+        os << m;
       return os.str();
     }
 
diff --git a/spot/twaalgos/dtwasat.cc b/spot/twaalgos/dtwasat.cc
index cab21b276..7d5037eca 100644
--- a/spot/twaalgos/dtwasat.cc
+++ b/spot/twaalgos/dtwasat.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2013-2018 Laboratoire de Recherche
+// Copyright (C) 2013-2019 Laboratoire de Recherche
 // et Développement de l'Epita.
 //
 // This file is part of Spot, a model checking library.
@@ -63,8 +63,6 @@ namespace spot
   namespace
   {
     static bdd_dict_ptr debug_dict = nullptr;
-    static const acc_cond* debug_ref_acc = nullptr;
-    static const acc_cond* debug_cand_acc = nullptr;
 
     struct path
     {
@@ -333,15 +331,14 @@ namespace spot
       std::string
       fmt_ta(unsigned src, bdd& cond, unsigned dst, unsigned nacc)
       {
-        return helper.format_ta(debug_dict, debug_cand_acc, src, cond,
-            dst, cacc.mark(nacc));
+        return helper.format_ta(debug_dict, src, cond, dst, cacc.mark(nacc));
       }
 
       std::string
       fmt_ta(unsigned src, unsigned cond, unsigned dst, unsigned nacc)
       {
-        return helper.format_ta(debug_dict, debug_cand_acc, src,
-            alpha_vect[cond], dst, cacc.mark(nacc));
+        return helper.format_ta(debug_dict, src,
+                                alpha_vect[cond], dst, cacc.mark(nacc));
       }
 
       std::string
@@ -349,8 +346,8 @@ namespace spot
           unsigned dst_ref, acc_cond::mark_t acc_cand = {},
           acc_cond::mark_t acc_ref = {})
       {
-        return helper.format_p(debug_cand_acc, debug_ref_acc, src_cand,
-            src_ref, dst_cand, dst_ref, acc_cand, acc_ref);
+        return helper.format_p(src_cand, src_ref, dst_cand, dst_ref,
+                               acc_cand, acc_ref);
       }
 
       acc_cond::mark_t
@@ -568,8 +565,6 @@ namespace spot
       assert(d.cand_size > 0);
 
 #if TRACE
-      debug_ref_acc = &ref->acc();
-      debug_cand_acc = &d.cacc;
       solver.comment("d.ref_size:", d.ref_size, '\n');
       solver.comment("d.cand_size:", d.cand_size, '\n');
 #endif
diff --git a/spot/twaalgos/emptiness.cc b/spot/twaalgos/emptiness.cc
index 30795f812..0f044c900 100644
--- a/spot/twaalgos/emptiness.cc
+++ b/spot/twaalgos/emptiness.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2009, 2011-2018 Laboratoire de Recherche et
+// Copyright (C) 2009, 2011-2019 Laboratoire de Recherche et
 // Développement de l'Epita (LRDE).
 // Copyright (C) 2004, 2005 Laboratoire d'Informatique de Paris 6 (LIP6),
 // département Systèmes Répartis Coopératifs (SRC), Université Pierre
@@ -632,7 +632,7 @@ namespace spot
               {
                 os << "ERROR: no transition with label="
                    << bdd_format_formula(aut->get_dict(), label)
-                   << " and acc=" << aut->acc().format(acc)
+                   << " and acc=" << acc
                    << " leaving state " << serial
                    << " for state " << aut->format_state(next) << '\n'
                    << "The following transitions leave state " << serial
@@ -644,9 +644,7 @@ namespace spot
                       os << "  * label="
                          << bdd_format_formula(aut->get_dict(),
                                                j->cond())
-                         << " and acc="
-                         << (aut->acc().format
-                             (j->acc()))
+                         << " and acc=" << j->acc()
                          << " going to " << aut->format_state(s2) << '\n';
                       s2->destroy();
                     }
@@ -660,20 +658,19 @@ namespace spot
           {
             os << "transition with label="
                << bdd_format_formula(aut->get_dict(), label)
-               << " and acc=" << aut->acc().format(acc)
-               << std::endl;
+               << " and acc=" << acc << std::endl;
           }
         else
           {
             os << "  |  ";
             bdd_print_formula(os, aut->get_dict(), label);
-            os << '\t';
-            aut->acc().format(acc);
+            if (acc)
+              os << '\t' << acc;
             os << std::endl;
           }
         aut->release_iter(j);
 
-        // Sum acceptance conditions.
+        // Sum acceptance marks.
         //
         // (Beware l and i designate the next step to consider.
         // Therefore if i is at the beginning of the cycle, `acc'
@@ -686,8 +683,8 @@ namespace spot
               {
                 all_acc_seen = true;
                 if (debug)
-                  os << "all acceptance conditions ("
-                     << aut->acc().format(all_acc)
+                  os << "all acceptance marks ("
+                     << all_acc
                      << ") have been seen\n";
               }
           }
@@ -696,10 +693,10 @@ namespace spot
     if (!aut->acc().accepting(all_acc))
       {
         if (debug)
-          os << "ERROR: The cycle's acceptance conditions ("
-             << aut->acc().format(all_acc)
-             << ") do not\nmatch those of the automaton ("
-             << aut->acc().format(aut->acc().all_sets())
+          os << "ERROR: The cycle's acceptance marks ("
+             << all_acc
+             << ") do not satisfy the acceptance condition ("
+             << aut->get_acceptance()
              << ")\n";
         return false;
       }
diff --git a/tests/core/acc.cc b/tests/core/acc.cc
index 9aa01b3a5..91e829724 100644
--- a/tests/core/acc.cc
+++ b/tests/core/acc.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-x
-// Copyright (C) 2014, 2015, 2017, 2018 Laboratoire de Recherche et
+// Copyright (C) 2014, 2015, 2017, 2018, 2019 Laboratoire de Recherche et
 // Développement de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -28,9 +28,7 @@
 
 static void check(spot::acc_cond& ac, spot::acc_cond::mark_t m)
 {
-  std::cout << '#' << m.count() << ": " << ac.format(m);
-  if (!m)
-    std::cout << "empty";
+  std::cout << '#' << m.count() << ": " << m;
   if (ac.accepting(m))
     std::cout << " accepting";
   std::cout << '\n';
diff --git a/tests/core/acc.test b/tests/core/acc.test
index 9a33a826f..ad7f80578 100755
--- a/tests/core/acc.test
+++ b/tests/core/acc.test
@@ -1,6 +1,6 @@
 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2014, 2015, 2017 Laboratoire de Recherche et
+# Copyright (C) 2014, 2015, 2017, 2019 Laboratoire de Recherche et
 # Développement de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -39,7 +39,7 @@ Inf(0)&Inf(1)&Inf(2)&Inf(3)
 #3: {0,2,3}
 #1: {0}
 #4: {0,1,2,3}
-#0: empty
+#0: {}
 #5: {0,1,2,3,4} accepting
 #2: {1,2}
 5 + 5 = 10
@@ -48,14 +48,14 @@ Inf(0)&Inf(1)&Inf(2)&Inf(3)
 #7: {0,1,2,3,4,6,7}
 #10: {0,1,2,3,4,5,6,7,8,9} accepting
 0,1,2,3,4,5,6,7,8,9
-#0: empty accepting
-#0: empty accepting
+#0: {} accepting
+#0: {} accepting
 #1: {3}
 #4: {0,1,2,3}
 #2: {0,2}
 stripping
 #2: {0,2}
-#0: empty
+#0: {}
 #2: {0,3}
 #1: {1}
 #2: {1,2}