A bound for divisible codes

A divisible code is a linear code whose word weights have a common divisor larger than one. If the divisor is a power of the field characteristic, there is a simple bound on the dimension of the code in terms of its weight range. When this bound is applied to the subcode of words with weight divisible by four in a type I binary self-dual code. It yields an asymptotic improvement of the Conway-Sloane bound for self-dual codes