let be A , B and C three non-commuting observables my question is how can one solve the problem with associative property ? i mean [tex] (AxB)xC [/tex] will in general be different from [tex] Ax(BxC) [/tex] and if we had 4 A, B ,C ,D instead of three the problem is even worse , how can anyone deal with it ?? i mean since the observable do not commute and we can not apply the associative property is there any ambiguity in QM ?? or similar ??