evaluated = naturalExpr.evaluate();
System.out.printf("%s = %s%n", naturalExpr, evaluated);
assertEquals(evaluated, N.create(42));
Expression equality = new Equality(naturalExpr, N.create(42));
evaluated = equality.evaluate();
System.out.printf("%s : %s%n", equality, evaluated);
assertEquals(evaluated, TruthValue.True);
Expression elementOf = new ElementOf(naturalExpr, N);
evaluated = elementOf.evaluate();