private void duellReaders(CompositeReader other, AtomicReader memIndexReader)
throws IOException {
AtomicReader competitor = new SlowCompositeReaderWrapper(other);
Fields memFields = memIndexReader.fields();
for (String field : competitor.fields()) {
Terms memTerms = memFields.terms(field);
Terms iwTerms = memIndexReader.terms(field);
if (iwTerms == null) {
assertNull(memTerms);
} else {