Problems which lead to a generalization of the concept of an ordinary nonlinear differential equation Kurzweil, J. — 1963 Differential Equations and Their Applications
A characterization of analytic operations in real Banach spaces J. Kurzweil — 1953 Studia Mathematica
On the metric theory of inhomogeneous diophantine approximations J. Kurzweil — 1955 Studia Mathematica