Used simplifier rules: insert-03: ⊦ st[a, d].keys = st.keys ++ a;%Keys: ⊦ a ∈ st.keys ↔ a ∈ st;%Min-min: ⊦ a ∈ st → ¬ a < st.min;%inf: ⊦ a ∈ st → a ∈ st.keys;% ⊦ s ++ a = s ↔ a ∈ s; (s)