λ (p q : Prop) (H1 : p) (H2 : q) (c : Prop) (H : p → q → c),
  H H1 H2 :
  ∀ (p q : Prop),
    p → q → (∀ (c : Prop), (p → q → c) → c)
let1.lean:19:19: error: type mismatch at term
  λ (p q : Prop) (H1 : p) (H2 : q) (c : Prop) (H : p → q → c),
    H H1 H2has type
  ∀ (p q : Prop),
    p → q → (∀ (c : Prop), (p → q → c) → c)
but is expected to have type
  ∀ (p q : Prop),
    p → q → (λ (p q : Prop), ∀ (c : Prop), (p → q → c) → c) q p