 Knizhnik–Zamolodchikov equations

In mathematical physics the Knizhnik–Zamolodchikov equations, or KZ equations, are linear differential equations satisfied by the correlation functions (on the Riemann sphere) of two-dimensional conformal field theories associated with an affine Lie algebra at a fixed level.They form a system of complex partial differential equations with regular singular points satisfied by the "N"-point functions of affine primary fields and can be derived using either the formalism of Lie algebras or that of vertex algebras.