s ⊆ s0 ⊦ ∃ s1. s ∪ s1 = s0 ∧ s ∩ s1 = ∅
Used simplifier rules: unsub: ⊦ s ⊆ s ∪ s0;%una: ⊦ (s ∪ s0) ∪ s1 = s ∪ s0 ∪ s1;%unc: ⊦ s ∪ s0 = s0 ∪ s;