Pencils of lines and the topology of real algebraic curves

Using a pencil of lines, a new restriction on the location of ovals of a nonsingular plane curve is obtained. It turns out that the location of a curve separating its complexification with respect to a pencil of lines determines to a significant degree the complex orientation of the curve. Furthermore, a new invariant of the strict isotopy type of the curve is given, which in particular distinguishes some seventh degree $M$-curves with the same complex scheme. A restriction on the complex orientation of seventh degree $M$-curves is proved.
Bibliography: 9 titles.