Two-sheeted coverings of real algebraic surfaces (Q1905342)

This very short paper (translated from Russian) studies the situation of a two-sheeted covering \(X\) of a non-singular real algebraic surface \(Y\) ramified along a non-singular real algebraic curve \(Z\). Several results are given, precising conditions for \(X\) to be an \(M\)-surface in terms of the topology of \(Y\) and \(Z\). The last two propositions consist of congruences modulo 8 relating some Euler characteristic with the number of self-intersections of \(Z\) in \(Y\) and based of the Gudkov-Krakhnov-Kharlamov congruences. The paper is too short to give fully detailed proofs. Notations are not always very clear.