An incompressible bounded
surface F on the boundary of a compact, connected, orientable 3-manifold M is
arc-extendible if there is a properly embedded arc γ on ∂M − IntF such that
F ∪ N(γ) is incompressible, where N(γ) is a regular neighborhood of γ in ∂M.
Suppose for simplicity that M is irreducible and F has no disk components. If M is a
product F × I, or if ∂M − F is a set of annuli, then clearly F is not arc-extendible.
The main theorem of this paper shows that these are the only obstructions for F to
be arc-extendible.