ANSI Common Lisp 15 Arrays 15.1 Array Concepts 15.1.1 Array Elements
220.127.116.11 Array Rank
An array can have any number of dimensions (including zero).
The number of dimensions is called the rank.
If the rank of an array is zero then the array is said to have
no dimensions, and the product of the dimensions (see array-total-size)
is then 1; a zero-rank array therefore has a single element.
18.104.22.168.2 Multidimensional Arrays