Set: pp::colors
  Set: pp::unicode
  Assumed: C
  Assumed: D
  Assumed: R
  Proved: R2
Theorem R2 (A A' B B' : Type) (H : (A → B) = (A' → B')) (a : A) : B = B' := R A A' (λ x : A, B) (λ x : A', B') H a
  Proved: R3
  Proved: R4
  Proved: R5
Theorem R5 (A1 A2 B1 B2 : Type) (H : (A1 → B1) = (A2 → B2)) (a : A1) : B1 = B2 :=
    R A1 A2 (λ x : A1, B1) (λ x : A2, B2) H a