# s < # s0 ⊦ ∃ a. a ∈ s0 ∧ ¬ a ∈ s
Used simplifier rules: sub-size: ⊦ s ⊆ s0 → ¬ # s0 < # s;% ⊦ m ≠ n → (m < n ↔ ¬ n < m); (ss) Used terms: s, s0