Solution
= Solution
The three-gamma matrix $C\gamma^{mnp}$ is antisymmetric, and for three distinct indices it is nonzero. A pair of nonzero Grassmann components therefore produces a nonzero term exactly as in the scalar case. Consequently this three-form bilinear is \b[not identically zero]. Equivalently it is dual to the axial-vector <Majorana spinor> bilinear, which is allowed; it must not be confused with the vanishing vector in part (a).