  It would seem that Yang’s comment is misleading since it suggests that Weyl did not have a good reason for his remark. In fact, however, Weyl’s statement was firmly based on a detailed analysis of the discrete symmetries \(\mathbf{C}, \mathbf{P}, \mathbf{T}\) and \(\mathbf{CPT}\).  Coleman and Korté (2001) have shown in detail that Weyl’s treatment of these symmetries is the same as that used today except for the fact that the symmetry \(\mathbf{T}\) is treated by Weyl as linear and unitary, rather than as antilinear and antiunitary. Weyl had presented in 1931 a complete analysis, in the context of the quantized Maxwell-Dirac field equations, of the discrete symmetries that are now called \(\mathbf{C}, \mathbf{P}, \mathbf{T}\) and \(\mathbf{CPT}\). His transformations \(\mathbf{C}\) and \(\mathbf{P}\) are the same as those used today. His transformations \(\mathbf{T}\) and \(\mathbf{CPT}\) are also very close to those used today except that Weyl’s transformations were linear and unitary rather than antilinear and antiunitary.  Moreover, Weyl drew two very important conclusions from his analysis of these discrete symmetries. First, Weyl announced that the important question of the arrow of time had been solved because the field equations were not invariant under his time-reversal transformation \(\mathbf{T}\). Second, Weyl pointed out that the invariance of the field equations under his charge-conjugation transformation \(\mathbf{C}\) implied that the mass of the ‘anti-electron’ is necessarily the same as that of the electron; moreover, Weyl’s result is the primary reason that Dirac (1931, 61) abandoned the assignment of the proton to the role of the anti-electron. Many years later Dirac (1977, 145) recalled: 