Muon::TwinTubeMap::HedgehogTray Node1 Muon::TwinTubeMap:: HedgehogTray + nTubesPerLay Node2 std::vector< HedgehogBoard Ptr > Node2->Node1 +cards Node3 std::shared_ptr< T > + operator->() Node3->Node2 +elements Node4 T Node4->Node3 +ptr