Singleton

A singleton is an array with bound 1. Equivalently, its shape consists entirely of 1s. It may have any rank. For example, all the following are singletons:


 * The scalar
 * The vector
 * The matrix
 * The three-dimensional array
 * The nested scalar

Whether an array  is a singleton can be determined with   or, less efficiently, with.

Every scalar  is a singleton, because , or alternatively.

Singletons may be subject to singleton extension.

Only simple Boolean singletons are valid representations of logical true and false for the purposes of control structures.