 More recently, Alisa Bokulich (2008, and 2009 [Other Internet Resources]) has argued that Bohr’s correspondence principle should be understood in terms of what she calls Bohr’s selection rule. This selection rule states that “the transition from a stationary state \(n'\) to another stationary state \(n''\) is allowed if and only if there exists a \(\tau\)th harmonic in the classical motion of the electron in the stationary state; if there is no \(\tau\)th harmonic in the classical motion, then transitions between stationary states whose separation is \(\tau\) are not allowed quantum mechanically” (Bokulich 2008, p. 85). Thus, the correspondence principle, on this reading of Bohr, is defined as the statement that each allowed quantum transition between stationary states corresponds to one harmonic component of the classical motion. She argues that the asymptotic agreements of frequencies and intensities emphasized by Jammer and Darrigol respectively are applications or consequences of the correspondence principle, but not the correspondence principle itself. Moreover, she argues that the selection rule interpretation of Bohr’s correspondence principle best makes sense of Bohr’s claims that the correspondence principle applies to small \(n\), that it is a law of quantum theory, and that it is formalized and preserved in matrix mechanics.