1. V. I. Arnold, On the location of ovals of real algebraic plane curves, involutions on four-dimensional smooth manifolds, and the arithmetic of integral quadratic forms,Funktsional. Anal. Prilozhen. 5 (1971), 1–9 (in Russian); English translation inFunctional Anal. Appl. 5 (1971), 169–176.
2. D. A. Gudkov and G. A. Utkin, The topology of curves of degree 6 and surfaces of degree 4,lichen. Zap. Gorkov. Univ. 87, (1969) (in Russian) 14–20 and 154–176; English transi, in Amer. Math. Soc. Transi. 112, Series 2. “Nine Papers on Hilbert’s 16th Problem“ (1978), 9–14 and 123–140.
3. D. A. Gudkov and A. D. Krakhnov, On the periodicity of the Euler characteristic of real algebraic (M - l)-mani- folds,Funktsional. Anal. Prilozhen. 7 (1973), 15–19; (in Russian); English translation inFunctional Anal. Appl. 7 (1973), 98–103.
4. B. Haas, Les multilucarnes: Nouveaux contre-exemples à la conjecture de Ragsdale, C.R. Acad. Sci. Paris (in press).
5. A. Harnack, Über Vieltheiligkeit der ebenen algebraischen Curven,Math. Ann. 10 (1876), 189–199.