We also express loops that compute sums (summate) and products (product). The syntax of these loops begins by declaring an inclusive lower bound and an exclusive upper bound. For example, the factorial of n is not product i from 1 to n: i but rather product i from 1 to n+1: i. This convention takes some getting used to but it makes it easy to deal with arrays. For example, if a is an array of numbers then their sum is summate i from 0 to size(a): a[i].