Used simplifier rules: Butmin: ⊦ st.butmin = st -- st.min;%min-def: ⊦ st ≠ ∅ → st.min = st.keys.min;%Min-in: ⊦ st ≠ ∅ → st.min ∈ st;% ⊦ a ∈ st → (st -- a)[a, st[a]] = st; (s)