memory perception looking searching kick_together carry_together leds sleep carry_together go_grasp perform_grasp avoid_walking avoid_walking perform_grasp looking reunite arm_tracking close_hand reunite obstacle_avoidance smart_walking looking random_head search_around smart_walking drop_ball smart_walking look_at slide_to walk_to turn_to Figure 7. The iterative development of the carry_together subtree of the reuniting application for Nao. In blue are leaf nodes. From bottom to top, trees of small size are created and debugged and then used as leaf nodes of trees of higher levels of abstraction. Other nodes of the full application, e.g., kick_together, are developed using a similar approach (but are omitted here for brevity). 58 * IEEE ROBOTICS & AUTOMATION MAGAZINE * september 2018