Bayer & McCreight (1972) considered the leaf level to be the lowest level of keys, but Knuth considered the leaf level to be one level below the lowest keys (Folk & Zoellick 1992, pp.  363).
Bayer & McCreight (1972) 认为叶子层是最下面一层的键，但是 Knuth 认为叶子层是最下面一层键之下的一层 （Folk & Zoellick 1992，p.363）。