it also converged to the tensor product Tsirelson bound , the most physically relevant one. Since one can produce a converging sequencing of approximations to from below by considering finite-dimensional states and observables, if , then this procedure can be combined with the NPA hierarchy to produce a halting algorithm to compute the Tsirelson bound, making it a computable number (note that in isolation neither procedure halts in general). Conversely, if is not computable, then . In January 2020, Ji, Natarajan, Vidick, Wright, and Yuen claimed to have proven that is not computable, thus solving Tsirelson's problem in the negative; a finalized, but still unreviewed, version of the proof appeared in Communications of the ACM in November 2021. Tsirelson's problem has been shown to be equivalent to Connes' embedding problem, so the same proof also implies that the Connes embedding problem is false. See also Quantum nonlocality Bell's theorem EPR paradox CHSH inequality Quantum pseudo-telepathy References Quantum measurement