I've been trying to use the following identity (provided by wikipedia) $$\epsilon^{i_1...i_n}\epsilon_{j_1...j_n} = \delta_{j_1...j_n}^{i_1...i_n} \equiv n!\delta_{[j_1}^{i_1}...\delta_{j_n]}^{i_n}$$ To prove the following relation in Peskin & Schroeder (p.134) $$\epsilon^{\alpha\beta\mu\nu}\ep...