@Override
 public void visit(Collection<? extends Proposition> propositions) {
   for (Proposition proposition : propositions) {
     proposition.accept(this);
   }
 }
 private void doWritePropId(Proposition proposition) throws IOException {
   StringUtil.escapeAndWriteDelimitedColumn(proposition.getId(), COLUMN_DELIMITER, this.writer);
   this.writer.write(COLUMN_DELIMITER);
 }