⊦ (a0 ∈ st -- a -- a → a0 ∈ st -- a) ∧ (st -- a -- a)[a0] = (st -- a)[a0]
Used simplifier rules: Del-in: ⊦ a ∈ st -- b ↔ a ≠ b ∧ a ∈ st;%Del-notin: ⊦ ¬ a ∈ st -- a;