On the Assmus–Mattson type theorem for Type I and even formally self-dual codes
In the present paper, we give the Assmus–Mattson type theorem for near-extremal Type I and even formally self-dual codes. We show the existence of 1-designs or 2-designs for these codes. As a corollary, we prove the uniqueness of a self-orthogonal 2-(16,6,8) design.
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