Notes to The Consistent Histories Approach to Quantum Mechanics

1. The expression (17) is sometimes ascribed to Wigner (1963, equation 12) and sometimes to Aharonov, Bergmann, & Lebowitz (1964). However, they were discussing the case where the system being described quantum mechanically by a wave function is subjected to a series of measurements by external devices which themselves are not part of this system and thus not part of the quantum mechanical description. Hence despite the formal resemblance the formulas given by these authors apply to a different physical situation from the one considered here.