code: public Interval<C> behind() {
          if(this.hasNone()) {
              return new Interval(this.dimension, Range.all());
          }
          if(this.range.equals(Range.all())) {
              return new Interval(this.dimension);
          }
          return new Interval(this.dimension,
                              Range.upTo(this.range.lowerEndpoint(),
                              reverse(this.range.lowerBoundType())));
      }
docs: Find the interval that extends behind this one.
  @return interval with lower endpoint equal to minus infinity and upper
  endpoint equal to this lower endpoint
  @see #ahead