| n ≤ #(a + x0), ∀ n. n ≤ # x0 → (x0 to n) + (x0 from n) = x0 ⊦ (a + x0 to n) + (a + x0 from n) = a + x0 |
n ≤ 1 + # x0, ∀ n. n ≤ # x0 → (x0 to n) + (x0 from n) = x0 ⊦ (a ' + x0 to n) + (a ' + x0 from n) = a ' + x0
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ # a ' = 0 +1; (s)% ⊦ #(x + y) = # x + # y; (s)% ⊦ a + x = a ' + x; (s)