intro s₁ s₂
case h
R : Type
inst✝² : Ring R
inst✝¹ : DecidableEq R
X : Type
inst✝ : DecidableEq X
a : R
x₁ x₂ : R[X]
⊢ ∀ (a_1 b : FormalSum R X),
    a • (Quotient.mk (formalSumSetoid R X) a_1 + Quotient.mk (formalSumSetoid R X) b) =
      a • Quotient.mk (formalSumSetoid R X) a_1 + a • Quotient.mk (formalSumSetoid R X) b
case h
R : Type
inst✝² : Ring R
inst✝¹ : DecidableEq R
X : Type
inst✝ : DecidableEq X
a : R
x₁ x₂ : R[X]
s₁ s₂ : FormalSum R X
⊢ a • (Quotient.mk (formalSumSetoid R X) s₁ + Quotient.mk (formalSumSetoid R X) s₂) =
    a • Quotient.mk (formalSumSetoid R X) s₁ + a • Quotient.mk (formalSumSetoid R X) s₂