[tlaplus] Writing temporal formula predicated on step not being taken

[Andrew Helwer <andrew.helwer@xxxxxxxxx>]

I'm modeling a simple eventually-consistent system. In general, eventually-consistent systems will eventually converge when writes stop happening. In my system, I model this with a variable called converge that is arbitrarily set to TRUE at some point which keeps further writes from happening, so I can write a simple liveness property like:

Liveness == converge ~> \A n, o \in Node : state[n] = state[o]

This is simple and fine and works well. However, it's a bit weird to keep an entire variable around just for this purpose. Is it possible to write a temporal formula that says "if a write step is never taken, then eventually the system converges"? Something like:

Liveness == []~[write]_vars ~> \A n, o \in Node : state[n] = state[o]

Andrew Helwer

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