docs: static void pruneIncorrectSize(List<List<EllipsesIntoClusters.Node>> clusters, int N) {
  		// prune clusters which can't be a member calibration target
  		for (int i = clusters.size()-1; i >= 0; i--) {
  			if( clusters.get(i).size() != N ) {
  				clusters.remove(i);
  			}
  		}
  	}