| a ∈ s1, a ∈ s0, s0 ⊆ s1 ⊦ # s1 = 0, # s0 = 0, s0 = ∅, s1 = ∅, ∀ a0. a0 ∈ s1 \ (s0 -- a) ↔ a0 ∈ (s1 \ s0) ++ a |
a ∈ s0, a ∈ s1, s0 ⊆ s1 ⊦ # s0 = 0, # s1 = 0, a0 ∈ s1 \ (s0 -- a) ↔ a0 = a ∨ a0 ∈ s1 \ s0, s0 = ∅, s1 = ∅
Used simplifier rules: ⊦ a ∈ s ++ b ↔ a = b ∨ a ∈ s; (s)