Set: pp::colors
  Set: pp::unicode
  Proved: T1
  Proved: T2
Theorem T2 (a b : Bool) : a ∨ b ⇒ b ∨ a :=
    Discharge (λ H : a ∨ b, DisjCases H (λ H : a, Disj2 b H) (λ H : b, Disj1 a H))