  The poles and zeros of a transfer function can be studied by various means.
The main motivation of the present paper is to give a state-space description
of the module theoretic definition of zeros introduced and analyzed by Wyman et
al. (1989, 1991). This analysis is carried out for proper transfer functions.
  The obtained explicit equations determined by the system matrices are used
for defining two inner functions to transform the original transfer function
into a square, invertible one via multiplication eliminating the "generic"
zeros corresponding to the kernel and the image of the transfer function.
  As it is well-known the zeros are connected to various invariant subspaces
arising in geometric control, see e.g. Aling and Schumacher (1984) for a
complete description. The connections to these subspaces are also mentioned in
the paper.
