Zero curvature conditions and conformal covariance

Two-dimensional zero curvature conditions with special emphasis on conformal properties are investigated in detail and the appearance of covariant higher order differential operators constructed in terms of a projective connection is elucidated. The analysis is based on the Kostant decomposition of simple Lie algebras in terms of representations with respect to their ``principal'' SL(2) subalgebra. Journal of Mathematical Physics is copyrighted by The American Institute of Physics