1. A : Type
2. B : Type
3. A List
4. u : A 5. v : A List
6. ys:(B List), x:A, y:B. (<x, y> zip(v;ys)) {(xv) & (yys)}
7. B List
8. u1 : B 9. v1 : B List
10. x:A, y:B. (<x, y> zip([u / v];v1)) {(x [u / v]) & (yv1)}
x:A, y:B. (<x, y> zip([u / v];[u1 / v1])) {(x [u / v]) & (y [u1 / v1])}