Complex sentence: The Landau gauge, obtained as the limit ξ → 0, is classically equivalent to Lorenz gauge, but postponing taking the limit until after the theory is quantized improves the rigor of certain existence and equivalence proofs.
Split into simpler sentences: The Landau gauge is classically equivalent to Lorenz gauge: it is obtained in the limit "ξ" → 0 but postpones taking that limit until after the theory has been quantized. It improves the rigor of certain existence and equivalence proofs.