In this paper, we propose to define the transfer function of a system
in a new way, namely as a semi-cancellable fraction (SCF), i.e., a fra
ction in which unstable pole-zero cancellations are not allowed. Withi
n this nerv framework, it is possible to be rigorous and coherent in d
ealing with the stabilizability of a system from an input-output viewp
oint, as opposed to recent papers focusing on the stabilizability of i
nfinite dimensional input-output systems.