st.keys = ∅, a ∈ st ⊦ a < st.min
Used simplifier rules: Keys: ⊦ a ∈ st.keys ↔ a ∈ st;%Min-min: ⊦ a ∈ st → ¬ a < st.min;%inf: ⊦ a ∈ st → a ∈ st.keys;