code: public boolean isRelation(DE9IMRelation.Type relationType) {
  		for (Type t : types) if (t.equals(relationType)) return true;
  		return false;
  	}
docs: Assess whether this relation is of a given {@link Type}.
  @param relationType The {@link Type} to compare against.
  @return <code>true</code> iff this relation is of the given {@link Type}.