+ e = numeric(1)/2 * z * (2*x + 2*y);
+ d = z * (x + y);
+ result += check_normal(e, d);
+
+ e = numeric(1)/6 * z * (3*x + 3*y) * (2*x + 2*w);
+ d = z * (x + y) * (x + w);
+ result += check_normal(e, d);
+
+ e = (3*x + 3*y) * (w/3 + z/3);
+ d = (x + y) * (w + z);
+ result += check_normal(e, d);
+