ABSTRACT
As the concept of BT has spread in the AI and robotics communities, a number of extensions have been proposed. Many of them revolve around the Fallback node, and the observation that the ordering of a Fallback node is often somewhat arbitrary. In the nominal case, the children of a Fallback node are different ways of achieving the same outcome, which makes the ordering itself unimportant, but note that this is not the case when Fallbacks are used to increase reactivity with implicit sequences, as described in Section 3.2.
