∀ a0. a0 ≠ b → (a0 = a ↔ a0 = c) ⊦ a = c, b ∈ ∅ ++ c
Used simplifier rules: in-04: ⊦ a ∈ ∅ ++ b ↔ a = b; Used formulas: b ∈ ∅ ++ c