⊦ (∅ ++ a ++ b).butmin.min = b, (∅ ++ a ++ b).butmin.min = a, a = b
Used simplifier rules: ⊦ a ∈ ∅ ++ b ↔ a = b; (s)% ⊦ a ∈ s ++ b ↔ a = b ∨ a ∈ s; (ws)