Jan Kisyński and Witold Tym. Sur la convergence des approximations successives pour l'équation ∂²z/∂x∂y = f(x, y, z, ∂z/∂x, ∂z/∂y). Annales Universitatis Mariae Curie-Skłodowska. Sectio A. Mathematica, 16:107-121 (1964), 1962.

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