Add a value to an element. The first element is at position 1 (1-based). Raise an exception if index <= 0 or index > f.sizeck/fenwick/size: forall<h> (f : fenwick<h>) -> (read<h>) int.

Create a Fenwick tree.

Return the sum from the first element to the end-th element (inclusive). The first element is at position 1 (1-based). For convenience, return 0 if end = 0. Raise an exception if end < 0 or end > f.sizeck/fenwick/size: forall<h> (f : fenwick<h>) -> (read<h>) int.