Unique negative dimension

Unique negative dimension (UND) is a complexity measure for the model of learning from positive examples. The unique negative dimension of a class $$C$$ of concepts is the size of the maximum subclass $$D\subseteq C$$ such that for every concept $$c\in D$$, we have $$\cap (D\setminus \{c\})\setminus c $$ is nonempty.

This concept was originally proposed by M. Gereb-Graus in "Complexity of learning from one-side examples", Technical Report TR-20-89, Harvard University Division of Engineering and Applied Science, 1989.