how does this new set relate to the more conventional formula_89 defined above? it can be proven that formula_106 is closed. moreover, formula_110, where formula_111 denotes the closure of formula_89. tsirelson’s problem consists in deciding whether the inclusion relation formula_110 is strict, i.e., whether or not formula_114. this problem only appears in infinite dimensions: when the hilbert space formula_96 in the definition of formula_106 is constrained to be finite-dimensional, the closure of the corresponding set equals formula_111.