On Binary Self-Dual Codes With Automorphisms

In this correspondence, we present some results concerning a decomposition of binary self-dual codes possessing an automorphism of certain type. Two applications are given. The first one is the classification of all extremal doubly even self-dual codes of length having an automorphism of order . The second one is the proof for uniqueness of the doubly even self-dual code having an automorphism of order .