  Behavior Trees (BT) are becoming increasingly popular in the robotics
community. The BT tool is well suited for decision-making applications allowing
a robot to perform complex behavior while being explainable to humans as well.
Verifying that BTs used are well constructed with respect to safety and
reliability requirements is essential, especially for robots operating in
critical environments. In this work, we propose a formal specification of
Behavior Trees and a methodology to prove invariants of already used trees,
while keeping the complexity of the formalization of the tree simple for the
final user. Allowing the possibility to test the particular instance of the
behavior tree without the necessity to know the more abstract levels of the
formalization.
