// Copied from org.eclipse.ocl.ecore.tests.DocumentationExamples.java

		// create an OCL helper object
		OCLHelper<EClassifier, EOperation, EStructuralFeature, Constraint> helper =
				ocl.createOCLHelper();

		// set the OCL context classifier
		helper.setContext(EXTLibraryPackage.Literals.LIBRARY);

		Constraint invariant = helper.createInvariant(
		    "books->forAll(b1, b2 | b1 <> b2 implies b1.title <> b2.title)");
		   
		OCLExpression<EClassifier> query = helper.createQuery(
		    "books->collect(b : Book | b.category)->asSet()");