1. Alling, N.L., Greenleaf, N.: Foundations of the theory of Klein surfaces. Lect. Notes in Math., vol. 219, Berlin-Heidelberg-New York: Springer 1971
2. Bujalance, E., Etayo, J.J.: A characterization ofq-hyperelliptic compact planar Klein surfaces (to appear)
3. Bujalance, J.A.: Normal subgroups of even index of an NEC group (to appear)
4. Etayo, J.J.: On the order of automorphism groups of Klein surfaces. Glasg. Math. J.26, 75?81 (1985)
5. Hoare, A.H.M., Singerman, D.: The orientability of subgroups of plane groups, in Groups-St. Andrews 1981, London Math. Soc. Lecture Note. Series71, 221?227 (1982)