  The envelope of holomorphy of an arbitrary domain in a two-dimensional Stein
manifold is identified with a connected component of the set of equivalence
classes of analytic discs immersed into the Stein manifold with boundary in the
domain. This implies, in particular, that for each of its points the envelope
of holomorphy contains an embedded (non-singular) Riemann surface (and also an
immersed analytic disc) passing through this point with boundary contained in
the natural embedding of the original domain into its envelope of holomorphy.
Moreover, it says, that analytic continuation to a neighbourhood of an
arbitrary point of the envelope of holomorphy can be performed by applying the
continuity principle once. Another corollary concerns representation of certain
elements of the fundamental group of the domain by boundaries of analytic
discs. A particular case is the following. Given a contact three-manifold with
Stein filling, any element of the fundamental group of the contact manifold
whose representatives are contractible in the filling can be represented by the
boundary of an immersed analytic disc.
