Korchagin's third conjecture

Abstract

We consider the $M$-curves of degree nine with three nests $1 \langle α_i \rangle, i = 1, 2, 3$ in $\mathbb{R}P^2$. After systematic constructions, Korchagin conjectured that at least two of the $α_i$ must be odd. It was later proved that there is always one odd $α_i$. We say that the curve has a jump in a non-empty oval $O$ if there exist four ovals $A, B, C, D$, with $A$ interior to some other non-empty oval $O'$, $D$ exterior, $B, C$ interior to $O$, such that $B$ and $C$ are separated inside of $O$ by any line passing through $A$ and $D$. In this paper, we prove the conjecture for the curves without jump, and we find restrictions on the complex orientations and rigid isotopy types admissible for the curves even, even, odd with jump.