Superinjective Simplicial Maps of Complexes of Curves and Injective Homomorphisms of Subgroups of Mapping Class Groups II

Original · EN

Let R be a compact, connected, orientable surface of genus g with p boundary components. Let C(R) be the complex of curves on R and Modᵣ* be the extended mapping class group of R. Suppose that either g = 2 and p > 1 or g > 2 and p >= 0. We prove that a simplicial map lambda from C(R) to C(R) is superinjective if and only if it is induced by a homeomorphism of R. As a corollary, we prove that if K is a finite index subgroup of Modᵣ* and f is an injective homomorphism from K to Modᵣ*, then f is induced by a homeomorphism of R and f has a unique extension to an automorphism of Modᵣ*. This extends the author's previous results about closed connected orientable surfaces of genus at least 3, to the surface R.