On Efimov's theorem on differential tests for a homeomorphism

The author obtains a new formulation of Efimov's differential condition which guarantees that a mapping $f\colon\mathbb R^2\to\mathbb R^2$ is a homeomorphism, and uses it to obtain, with the aid of the Hadamard–Lévy–John global inverse function theorem, differential conditions under which f is not only injective but also surjective.