| #(s0 \ s) = # s0 - # s, a ∈ s0, a0 ∈ s0, # s0 < # s, a1 ∈ s, a2 ∈ s, ∀ a0. a0 ∈ s ++ a → a0 ∈ s0 ⊦ # s0 - # s - 1 = # s0 - # s + 1, a1 ∈ s0, a ∈ s, a1 ∈ s ++ a |
Used simplifier rules: In-insert: ⊦ a ∈ s ++ b ↔ a = b ∨ a ∈ s; from specification set-basic%n ≤ m ⊦ n0 = m - n ↔ m = n0 + n; (elim) Used terms: # s0 - # s, 1, n