The importance of the alternating tensor follows from the fact that it is the only isotropic, 3rd-order tensor1. Appendix C shows that a 3rd-order tensor can be isotropic only if it is completely antisymmetric, meaning it changes sign when any two of its three indices are interchanged. In this appendix, we will see how this property of complete antisymmetry defines the Levi-Civita tensor. We will then see how some fundamental operations in algebra follow from it.
1up to a multiplicative constant.