constructor
f g : Vars →₀ ℕ
⊢ (∀ (x : Vars), f x = g x) ↔ f α = g α ∧ f β = g β
case mp
f g : Vars →₀ ℕ
⊢ (∀ (x : Vars), f x = g x) → f α = g α ∧ f β = g β

case mpr
f g : Vars →₀ ℕ
⊢ f α = g α ∧ f β = g β → ∀ (x : Vars), f x = g x