| # (m ≤ # x ⊃ firstn(m, x);x) < n ⊦ x = ((n < m ⊃ n;m) ≤ # x ⊃ firstn((n < m ⊃ n;m), x);x), m ≤ # x |
# x < m, # x < n ⊦ x = ((n < m ⊃ n;m) ≤ # x ⊃ firstn(n, x);x)
Used simplifier rules: ⊦ m < n → (n ≤ m ↔ false); (s)% ⊦ m < n → n ≠ 0; (s)%f: ⊦ m < n → n ≠ 0; (forward) from specification nat-basic% ⊦ m ≤ n ↔ ¬ n < m; (ss)