This paper is the first step in the
solution of the problem of finite completion of comma-free codes.
We show that every finite comma-free code is included in a
finite comma-free code of particular kind, which we called, for
lack of a better term,
canonical comma-free code. Certainly, finite maximal comma-free codes
are always canonical. The final step of the solution which consists
in proving further that every canonical comma-free code is completed
to a finite
maximal comma-free code, is intended to be published in a forthcoming
paper.