Valve released a massive update to its in-development MOBA hero shooter Deadlock, adding six new heroes, map changes, and engine improvements that propelled the game to over 220,000 concurrent players. The update makes Deadlock the sixth most-played game on Steam, though it remains in limited early access via friend invites.
The article explores how reachability properties—whether a system state is reachable—can be expressed and verified in TLA⁺, a formal specification language. It explains that TLA⁺ already supports basic reachability via the ENABLED operator, discusses Lamport's more general approach using concatenated actions, and describes TLC's recent addition of the _POSSIBLE operator for checking if a property can be satisfied from initial states.