1. Birman, J.S.: Braids, links, and mapping class groups. Ann. Math. Stud.82, (1974)
2. Birman, J.S., Hilden, H.M.: On the mapping class groups of closed surfaces as covering spaces. In: Advances in the theory of Riemann surfaces. Ann. Math. Stud.66, 81?115 (1971)
3. Bleiler, A.S., Moriah, Y.: Heegaard splittings and branched coverings of B3. Math. Ann.281, 531?543 (1988)
4. Boileau, M., Collins, D.J., Zieschang, H.: Scindements de Heegaard des petites variétés de Seifert. C.R. Acad. Sci. Paris303-I, 557?560 (1987)
5. Boileau, M., Collins, D.J., Zieschang, H.: Genus 2 Heegaard decompositions of small Seifert manifolds. Preprint