diff --git a/ChangeLog b/ChangeLog
index 9188ddca4..b5468de3f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2004-07-07  Alexandre Duret-Lutz  <adl@src.lip6.fr>
+
+	* src/tgbaalgos/gtec/gtec.hh (emptiness_check_shy::find_state): Add
+	comments.
+	* iface/gspn/ssp.cc (emptiness_check_shy_ssp::find_state): Likewise.
+	Soheib and I had a hard time figuring why we did this...
+
 2004-07-02  Thomas Martinez  <martinez@src.lip6.fr>
 
 	* src/tgba/tgbareduc.cc, src/tgba/tgbareduc.hh,
diff --git a/iface/gspn/ssp.cc b/iface/gspn/ssp.cc
index 81d820916..5b6a950bd 100644
--- a/iface/gspn/ssp.cc
+++ b/iface/gspn/ssp.cc
@@ -909,6 +909,11 @@ namespace spot
     }
 
   protected:
+
+    // If a new state includes an older state, we may have to add new
+    // children to the list of children of that older state.  We cannot
+    // to this by sub-classing numbered_state_heap since TODO is not
+    // available.  So we override find_state() instead.
     virtual int*
     find_state(const state* s)
     {
diff --git a/src/tgbaalgos/gtec/gtec.hh b/src/tgbaalgos/gtec/gtec.hh
index 22dbfec8e..032186c8b 100644
--- a/src/tgbaalgos/gtec/gtec.hh
+++ b/src/tgbaalgos/gtec/gtec.hh
@@ -135,6 +135,14 @@ namespace spot
     typedef std::pair<const state*, succ_queue> pair_state_successors;
     std::stack<pair_state_successors> todo;
 
+    /// \brief find the SCC number of a unprocessed state.
+    ///
+    /// Sometimes we want to modify some of the above structures when
+    /// looking up a new state.  This happens for instance when find()
+    /// must perform inclusion checking and add new states to process
+    /// to TODO during this step.  (Because TODO must be known,
+    /// sub-classing spot::numbered_state_heap is not enough.)  Then
+    /// overriding this method is the way to go.
     virtual int* find_state(const state* s);
   };