| a ∈ s0, a ∈ s1 ⊦ #(s0 ∪ s1) < # s0 + # s1 |
a ∈ s0, a ∈ s1, a0 ∈ s0, a1 ∈ s1, # s0 + # s1 ≤ #(s0 ∪ s1) ⊦
Used simplifier rules: ⊦ ¬ a ∈ ∅; (s)% ⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2); (s)%ne-01: ⊦ a ∈ s → s ≠ ∅; (forward) from specification set-basic% ⊦ m < n ↔ ¬ n ≤ m; (ss)