Suppose that is an array of numbers. Then gives its average. Reading "right-to-left", gives the number of elements in X, and since is a dyadic operator, the term to its left is required as well. It is in parenthesis since otherwise X would be taken (so that the summation would be of , of each element of X divided by the number of elements in X), and adds all the elements of X. Building on this, calculates the standard deviation. Further, since assignment is an operator, it can appear within an expression, so