  Bidirected graphs are a generalisation of directed graphs that arises in the
study of undirected graphs with perfect matchings. Menger's famous theorem -
the minimum size of a set separating two vertex sets $X$ and $Y$ is the same as
the maximum number of disjoint paths connecting them - is generally not true in
bidirected graphs. We introduce a sufficient condition for $X$ and $Y$ which
yields a version of Menger's Theorem in bidirected graphs that in particular
implies its directed counterpart.
