elk-owl-parent/elk-owl-model/src/main/java/org/semanticweb/elk/owl/predefined/PredefinedElkIris.java
public static int compare(ElkIri firstIri, ElkIri secondIri) {
		boolean isOwl0 = firstIri.equals(OWL_THING)
				|| firstIri.equals(OWL_NOTHING);
		boolean isOwl1 = secondIri.equals(OWL_THING)
				|| secondIri.equals(OWL_NOTHING);

		if (isOwl0 == isOwl1)
			return firstIri.compareTo(secondIri);
		// else
		return isOwl0 ? -1 : 1;
	}
public static int compare(ElkIri firstIri, ElkIri secondIri) {
		boolean isOwl0 = firstIri.equals(OWL_THING)
				|| firstIri.equals(OWL_NOTHING);
		boolean isOwl1 = secondIri.equals(OWL_THING)
				|| secondIri.equals(OWL_NOTHING);

		if (isOwl0 == isOwl1)
			return firstIri.compareTo(secondIri);
		// else
		return isOwl0 ? -1 : 1;
	}
Defines an ordering on IRIs starting with {@link #OWL_NOTHING},
{@link #OWL_THING}, followed by the remaining IRIs in alphabetical order.

@param firstIri
the fist {@link ElkIri} to compare with the second
@param secondIri
the second {@link ElkIri} to compare with the first
@return a negative integer, zero, or a positive integer as the first IRI
is less, equal, or greater than the second IRI in the specified
order