}
protected TextRulerStatisticsCollector getCoveringIntersection(
final TextRulerStatisticsCollector c1, final TextRulerStatisticsCollector c2) {
// calculate intersections of coverings:
TextRulerStatisticsCollector resultC = new TextRulerStatisticsCollector(c1);
resultC.getCoveredPositiveExamples().retainAll(c2.getCoveredPositiveExamples());
resultC.getCoveredNegativeExamples().retainAll(c2.getCoveredNegativeExamples());
resultC.reflectCountsFromCoveredExamples();
return resultC;
}