  A classic result due to Douglas establishes that, for odd spread $k$ and
dimension $d=\frac{1}{2}(3k+3)$, all maximum length $(d,k)$ circuit codes are
isomorphic. Using a recent result of Byrnes we extend Douglas's theorem to
prove that, for $k$ even $\ge 4$ and $d=\frac{1}{2}(3k+4)$, all maximum length
symmetric $(d,k)$ circuit codes are isomorphic.
