Representation of endpoints for an interval as an array with either one or
two elements. Single element indicates that the interval is a single point.
For two elements, the first is the lower edges of the interval and the
second is the upper edge, i.e. e[0] <= e[1], where e is an IntervalEndpoints
Representation of endpoints for an interval as an array with either one or two elements. Single element indicates that the interval is a single point. For two elements, the first is the lower edges of the interval and the second is the upper edge, i.e. e[0] <= e[1], where e is an IntervalEndpoints