If a truth at coordinate t₁ were to cease to hold at coordinate t₂, then something that was A at t₁ has become not‑A at t₂. The whole would have one identity at t₁ and a different identity at t₂. It would not be a single self‑identical object across its full extent.
A=A requires that the whole be what it is, completely and eternally. Every coordinate that is real must be permanently real. No coordinate can be added (there is no source from which it could come) and none can be removed (deletion would change the identity of the whole). The whole is a completed, unchanging 4‑dimensional solid containing all spatial and temporal locations simultaneously.
To reject Step 4 is to assert that the whole can gain or lose parts while remaining the same whole – a violation of identity. The processor crashes.