  Robot missions typically involve a number of desired objectives, such as
avoiding collisions, staying connected to other robots, gathering information
using sensors and returning to the charging station before the battery runs
out. Some of these objectives need to be taken into account at the same time,
such as avoiding collisions and staying connected, while others are focused
upon during different parts of the executions, such as returning to the
charging station and connectivity maintenance.
  In this paper, we show how Control Barrier Functions(CBFs) and Behavior
Trees(BTs) can be combined in a principled manner to achieve both types of task
compositions, with performance guarantees in terms of mission completion. We
illustrate our method with a simulated underwater coverage mission.
