⌜# x⌝ = # σ1, ∀ n. n < # x → x[n] = σ1[n] ⊦ ⌜x⌝ = σ1
Used simplifier rules: size-fin: ⊦ # ⌜x⌝ = ⌜# x⌝ ;%sel-fin: ⊦ ⌜x⌝ [n] = x[n];%less-fin: ⊦ ⌜m⌝ < ⌜n⌝ ↔ m < n; from specification nat-inf