∀ {Γ : Subgroup (GL (Fin 2) ℝ)} {h : ℝ} [inst : Γ.HasDetPlusMinusOne],
  0 < h →
    h ∈ Γ.strictPeriods →
      ∀ (a b : ℤ) (f : ModularForm Γ a) (g : ModularForm Γ b),
        ModularFormClass.qExpansion h
            ⇑(((DirectSum.of (ModularForm Γ) a) f * (DirectSum.of (ModularForm Γ) b) g) (a + b)) =
          ModularFormClass.qExpansion h ⇑f * ModularFormClass.qExpansion h ⇑g