 A second consequence is that each LoA as a functional level provides correctness criteria for lower levels (Primiero 2020). Not just at the implementation level, correctness is required at any LoA from specification to execution, and the cause of malfunctions may be located at any LoA not correctly implementing its proper functional level (see  §7.3 and  Fresco, Primiero (2013)). According to Turner (2018), the specification level can be said to be correct or incorrect with respect to intentions, despite the difficulty of verifying their correctness. Correctness of any non-physical layer can be verified mathematically through formal verification, and the execution physical level can be verified empirically, through testing  (§6).  Verifying correctness of specifications with respect to clients’ intentions would require instead having access to the mental states of the involved agents.