formula_36, upon measuring formula_46, sends the spin system in the state formula_124 to formula_38. When now formula_38 measures formula_1 in the formula_128-basis, formula_36knows (by using quantum theory (Q)) that both outcomes are possible for formula_38's measurement. This again means that formula_36 knows (again by (Q)) that the combined system formula_81 of formula_1 and formula_38 will appear to an outside observer like formula_39 as the superposition formula_136. As this is precisely the formula_137 state of formula_39's measurement basis, formula_36 knows that "formula_39" will measure formula_89.