Peel the last summand off a sum over List.range.
A sum over List.range 2 in closed form.
A sum over List.range 3 in closed form.
A constant sum over List.range.
A sum of values at most one over List.range m is at
most m.
A vanishing sum over List.range has every summand
zero.
The window sizes of a list of intervals split into the excesses plus the number of intervals.
The excesses of a list of intervals sum to at least the number of nontrivial ones.