Here formula_38 is the 4-current, formula_39 is the field strength tensor (written as a 4 × 4 matrix), formula_40 is the Levi-Civita symbol, and formula_41 is the 4-gradient (so that formula_42 is the d'Alembertian operator). (The formula_43 in the first equation is implicitly summed over, according to Einstein notation.) The first tensor equation says the same thing as the two inhomogeneous Maxwell's equations: Gauss' law and Ampere's law with Maxwell's correction. The second equation say the same thing as the other two equations, the homogeneous equations: Faraday's law of induction and the absence of magnetic monopoles.