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 ${\displaystyle C}$ of concepts is the size of the maximum subclass ${\displaystyle D\subseteq C}$ such that for every concept ${\displaystyle c\in D}$, we have ${\displaystyle \cap (D\setminus \{c\})\setminus c}$ 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.