diff --git a/doc/notes b/doc/notes
index 4b32d0cb60b0264dafb1afdd19cac7c1a92e36ad..0e69a169b9ed283a354b75eca6b5ff8ca7299b81 100644
--- a/doc/notes
+++ b/doc/notes
@@ -24,6 +24,8 @@ In include/hpp/fcl/traversal:
     - bool initialize(MeshCollisionTraversalNodekIOS& node, ...
     - bool initialize(MeshCollisionTraversalNodeOBBRSS& node, ...
 
+-------------------------------------------------------------------------------
+
 classes
   - MeshCollisionTraversalNodeRSS,
   - MeshCollisionTraversalNodekIOS,
@@ -35,3 +37,11 @@ derive from
 They store the relative position and orientation between two objects to test for
 collision. before calling overlap function, this additional information computes
 the relative positions of the bounding volumes.
+
+-------------------------------------------------------------------------------
+
+For primitive shapes, collision and distance computation are very close.
+ShapeShapeCollide calls indeed ShapeShapeDistance. It would be convenient to
+merge CollisionRequest and DistanceRequest on the one hand and CollisionResult
+and DistanceResult on the other hand into two classes InteractionRequest and
+InteractionResult.
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