  As shown in earlier work, skew-adjoint linear differential operators, mapping
efforts into flows, give rise to Dirac structures on a bounded spatial domain
by a proper definition of boundary variables. In the present paper this is
extended to pairs of linear differential operators defining a formally
skew-adjoint relation between flows and efforts. Furthermore it is shown how
the underlying repeated integration by parts operation can be streamlined by
the use of two-variable polynomial calculus. Dirac structures defined by
formally skew adjoint operators and differential operator effort constraints
are treated within the same framework. Finally it is sketched how the approach
can be also used for Lagrangian subspaces on bounded domains.
