Different Perspectives on FLP Impossibility

TL;DR

The paper reconsiders the FLP impossibility by introducing a termination paradigm that decouples termination from the final binary decision and relies on initial-input agreement. It provides a crash-tolerant vector consensus algorithm in a fully asynchronous setting and proves unconditional termination along with safety, liveness, and validity. By showing that binary consensus can be derived from vector consensus through a fixed tie-interpretation, it demonstrates that termination of consensus does not imply impossibility in asynchronous systems. These results collectively challenge conventional interpretations of FLP and suggest new pathways toward robust distributed coordination under asynchrony.

Abstract

We demonstrate termination of binary consensus under the model and conditions used by Fischer, Lynch, and Patterson (FLP) to prove impossibility of binary agreement - in complete asynchrony and a possible process crash - in two steps. First, we introduce a new paradigm for consensus termination and show that impossibility of agreement is not evidence for impossibility to terminate. Next, we present a consensus algorithm that ensures termination with agreement about the initial input from the processes.