An extremely useful relation between the Kronecker delta and the Levi-Civita symbol.
The brackets mean that we completely anti-symmetrize in the indices m,npic.twitter.com/Hp8tK8qZ3D
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Abstract indices do not "run over" anything. The right-hand side here is the identity map on the space of 2-forms and the left-hand side is a projection mapping on the space of 2-forms, with 1-dimensional range. These can coincide only when the space of 2-forms is 1-dimensional.