M. Langer and H. Woracek,
A characterization of intermediate Weyl coefficients,
Monatsh. Math. 135 (2002), 137–155
Abstract:
In connection with an indefinite analogue of canonical systems
of differential equations some subclasses
N0/Δ (Δ∈ℕ0)
of the Nevanlinna class N0 come up.
We give a criterion for a function to belong to N0/Δ
in terms of its poles and residues.