| (s0 \ s1) ∩ s = ∅, (s2 \ s0) ∩ s = ∅, a ∈ s2, a ∈ s ⊦ s2 = ∅, s = ∅, #((s2 \ s1) ∩ s) = 0, # s2 = 0, # s = 0, a ∈ s1 |
⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2)
(s0 \ s1) ∩ s = ∅, ∀ a. a ∈ (s2 \ s0) ∩ s ↔ a ∈ ∅, a ∈ s2, a ∈ s ⊦ s2 = ∅, s = ∅, #((s2 \ s1) ∩ s) = 0, # s2 = 0, # s = 0, a ∈ s1
Used terms: ∅, (s2 \ s0) ∩ s