  Recently, a detailed epistemic reasoning framework for multi-agent systems
with byzantine faulty asynchronous agents and possibly unreliable communication
was introduced. We have developed a modular extension framework implemented on
top of it, which allows to encode and safely combine additional system
assumptions commonly used in the modeling and analysis of fault-tolerant
distributed systems, like reliable communication, time-bounded communication,
multicasting, synchronous and lock-step synchronous agents and even agents with
coordinated actions. We use this extension framework for analyzing basic
properties of synchronous and lock-step synchronous agents, such as the agents'
local and global fault detection abilities. Moreover, we show that even the
perfectly synchronized clocks available in lock-step synchronous systems cannot
be used to avoid "brain-in-a-vat" scenarios.
