// Copied from org.eclipse.ocl.examples.test.xtext.PivotDocumentationExamples.java

		// only print the set of book categories for valid libraries
		for (Library next : constraintEval.selectEcore(libraries)) {
		    @SuppressWarnings("unchecked")
		    Set<BookCategory> categories = (Set<BookCategory>) queryEval.evaluateUnboxed(next);
		    
		    debugPrintf("%s: %s%n\n", next.getName(), categories);
		}