The classification of unitals with parameters 2-(28, 4, 1) according to the 2-rank of their incidence matrices was initiated by McGuire, Tonchev and Ward, who proved that the 2-rank of any unital on 28 points is greater than or equal to 19, and up to isomorphism, there is a unique unital with 2-rank equal to 19. Jaffe and Tonchev investigated the next two 2-ranks, 20 and 21, and showed that there are no unitals on 28 points with 2-rank equal to 20, and there are exactly 4 isomorphism classes of unitals of rank 21. The subject of this paper is the classification of unitals having 2-rank 22, 23 and 24.

McGuire、Tonchev 和 Ward 提出了根据其关联矩阵的 2 秩对参数为 2-(28, 4, 1) 的单位进行分类，他们证明了任何单位在 28 个点上的 2 秩大于或等于 19，并且直到同构，有一个 2 秩等于 19 的唯一单位。Jaffe 和 Tonchev 研究了接下来的两个 2 秩，20 和 21，并表明在 28 点上没有单位 2 -rank 等于 20，并且恰好有 4 个 21 级单位的同构类。本文的主题是具有 2 级 22、23 和 24 的单位的分类。