func (r Region) IsGroup() bool {
	if r == 0 {
		return false
	}
	return int(regionInclusion[r]) < len(regionContainment)
}

// Contains returns whether Region c is contained by Region r. It returns true
// if c == r.
func (r Region) Contains(c Region) bool {
	if r == c {
		return true
	}
	g := regionInclusion[r]
	if g >= nRegionGroups {
		return false
	}
	m := regionContainment[g]