F̃^µν = (1/2)ε^µναβ F_αβ; source-free Maxwell = ∂_µ F̃^µν = 0 (Bianchi identity). Electric-magnetic duality for source-free fields.
F̃^µν = (1/2)ε^µναβ F_αβ; source-free Maxwell = ∂_µ F̃^µν = 0 (Bianchi identity). Electric-magnetic duality for source-free fields.