# s0 = 1, s ⊆ s0 ⊦ # s = 0, s = s0, s = ∅
Used simplifier rules: sub-idem: ⊦ s ⊆ s;%size-zero-01: ⊦ s ≠ ∅ → # s ≠ 0;%size-zero: ⊦ # s ≠ 0 → s ≠ ∅;