| 0 ≤ i ∧ 0 ≤ j, ∀ j0, i. i→n(j0) < i→n(j) → 0 ≤ i ∧ 0 ≤ j0 → fac(i + j0) = fac(i) * Π countFun(1, j0, λ j0. i + j0) ⊦ fac(i + j) = fac(i) * Π countFun(1, j, λ j0. i + j0) |
0 ≤ j, 0 ≤ i, ∀ j0, i. i→n(j0) < i→n(j) → 0 ≤ i ∧ 0 ≤ j0 → fac(i + j0) = fac(i) * Π countFun(1, j0, λ j0. i + j0) ⊦ fac(i + j) = fac(i) * Π countFun(1, j, λ j0. i + j0)