static IEnumerable <Point3d> PointsInSpace(ImmutableHashSet <Point3d> active)
{
var ranges = PointHelpers.FindSpaceOfPoints(active, Point3d.NumberOfDimensions)
.Select(r => new DimensionRange(r.Min - 1, r.Max + 1))
.ToImmutableArray();
return(PointHelpers.PointsInSpace(ranges, dim => new Point3d(dim.ToImmutableArray())));
}