“…The three-particle formalism has been derived following three different approaches: 2 (i) generic relativistic effective field theory (RFT) [3-5, 9-11, 15, 16, 18, 22, 24], (ii) nonrelativistic effective field theory (NREFT) [6,7,12,19,23,45], and (iii) (relativistic) finite volume unitarity (FVU) [8,26,29,36]. The equivalence of the RFT and FVU approaches, aside from some technical issues, has been shown in ref.…”