A Pos is a position in between two elements in a list. For example, position 0 marks the beginning of the list, and position length list marks the end of the list. There are n + 1 valid positions for a list of length n.

A range's positions mark the begin and end of a sublist, respectively.

Something that knows its range as sublist in a larger list. Minimal complete definition: either range or both begin and end.

distRange (b1, e1) (b2, e2) is defined as |b1 - b2| + |e1 - e2|.

Whether a position falls within a range, including the range's edges.

Yields whether the second argument completely falls within the first argument.

unionRange x y yields the smallest range z such that x `includes` z and y `includes` z.

A range's size is the number of elements it contains.

A range is valid if its positions are nonnegative and begin < end.