| c ∈ ∅ ++ a ++ b, c ∈ ∅ ++ c ++ b, ∀ a0. a0 ∈ ∅ ++ a ++ b ↔ a0 ∈ ∅ ++ c ++ b ⊦ a = c, b = c |
Used simplifier rules: in-04: ⊦ a ∈ ∅ ++ b ↔ a = b;%In-insert: ⊦ a ∈ s ++ b ↔ a = b ∨ a ∈ s;%In-insert: ⊦ a ∈ s ++ b ↔ a = b ∨ a ∈ s;%in-04: ⊦ a ∈ ∅ ++ b ↔ a = b; Used formulas: b ∈ ∅ ++ a