%AAlistarh, Dan%AAspnes, James%AEllen, Faith%AGelashvili, Rati%AZhu, Leqi%D2019%I
%K
%MOSTI ID: 10120533
%PMedium: X
%TWhy extension-based proofs fail
%XIt is impossible to deterministically solve wait-free consensus in an asynchronous system. The classic proof uses a valency argument, which constructs an infinite execution by repeatedly extending a finite execution. We introduce extension-based proofs, a class of impossibility proofs that are modelled as an interaction between a prover and a protocol and that include valency arguments.
Using proofs based on combinatorial topology, it has been shown that it is impossible to deterministically solve k-set agreement among n > k ≥ 2 processes in a wait-free manner. However, it was unknown whether proofs based on simpler techniques were possible. We show that this impossibility result cannot be obtained by an extension-based proof and, hence, extension-based proofs are limited in power.
Country unknown/Code not availablehttps://doi.org/10.1145/3313276.3316407OSTI-MSA