⊦ ⌜nf⌝ from n = ⌜nf from n⌝
⊦ ⌜(λ n. (n = 0 ⊃ a;nf(n -1))) from n + 1⌝ = ⌜nf⌝ from n
Used terms: n + 1, λ n. (n = 0 ⊃ a;nf(n -1))