⊦ ⌜nf(0) '⌝ + ⌜λ n. nf(n + 1)⌝ = ⌜nf⌝
Used simplifier rules: tl-inf: ⊦ tl(⌜nf⌝ ) = ⌜λ n. nf(n +1)⌝ ;%succ: ⊦ m +1 = m + 1; from specification nat-basic2