tst₁ : Π (A : Type), A → A
tst₂ : Π {A : Type}, A → A
symm₂ : ∀ {A : Type} (a b : A), a = b → b = a
tst₃ : Π (A : Type), A → A
foo : ∀ {A : Type} {a b : A}, a = b → (∀ (c : A), c = b → c = a)