⌜nσ[n]⌝ = leninv(nσ), m + 1 = nσ[n], ⌜n⌝ < # nσ, stutf(nσ) ⊦ nσ[n] = 0, # nσ = ∞ ∧ (n < m0 ∧ ⌜m0⌝ < # nσ → nσ[m0] = nσ[n])