code: @Override
      public boolean execute(Interval lhs, Interval rhs) {
          if (this.relation == null) {
              return false;
          } else {
              return this.relation.hasRelation(lhs, rhs);
          }
      }
docs: Executes the gap function. If the first interval (<code>lhs</code>) is
  before the second (<code>rhs</code>) and the distance between them is
  less than or equal to the <code>maximumGap</code>, then
  this method returns <code>true</code>, otherwise it returns
  <code>false</code>.
  
  @param lhs the first {@link Interval}.
  @param rhs the second {@link Interval}.
  @return <code>true</code> or <code>false</code>.