code: public int solutionHashCode() {
          return new HashCodeBuilder()
                  .append(id)
                  .append(homeTeam)
                  .append(awayTeam)
                  .append(day)
                  .toHashCode();
      }
docs: The normal methods {@link #equals(Object)} and {@link #hashCode()} cannot be used
  because the rule engine already requires them (for performance in their original state).
  @see #solutionEquals(Object)