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(1974, J. London Math. Soc. 2, 160-164) showed that outer automorphism groups of fundamental groups of closed orientable surfaces are residually finite. Here we generalize her result by showing that outer automorphism groups of generalized free products of two free groups amalgamating a maximal cyclic subgroup are residually finite. From this it follows that mapping class groups of closed orientable and nonorientable surfaces are residually finite. The latter answers a question raised by A. M. Gaglione.  2001 Elsevier Science

Abstract. In this paper it is shown that if the Frattini subgroup of the fundamental group of a compact, orientable, irreducible, sufficiently large 3-manifold is nontrivial then the 3-manifold is a Seifert fibered space. We show further that the Frattini subgroup of the group of a Seifert fibered space is trivial or cyclic. As a corollary to our work we prove that every knot group has trivial Frattini subgroup.