code: @Override
      public String format(Long position) {
          Date date = AbsoluteTimeGranularityUtil.asDate(position);
          return DATE_FORMAT.get().format(date);
      }
docs: Formats positions with a granularity of
  {@link org.protempa.proposition.value.AbsoluteTimeGranularity} with at
  least a granularity of DAY into an number with format
  <code>yyyyMMdd</code>.
  
  @param position a position {@link Long} with a granularity of
  {@link org.protempa.proposition.value.AbsoluteTimeGranularity}.
  @return a {@link String} with format <code>yyyyMMdd</code>.