English
The product of two ContMDiff maps is again ContMDiff; this is a basic property of smooth multiplication on a monoid.
Русский
Произведение двух ContMDiff отображений снова ContMDiff; это базовое свойство гладкого умножения в моноиде.
LaTeX
$$$ContMDiff I I n f \\\\land ContMDiff I I n g \\\\Rightarrow ContMDiff I I n (\\\\lambda x, f(x)\\\\cdot g(x))$$$
Lean4
/-- The composition of `C^n` functions is `C^n`. -/
theorem comp {g : M' → M''} (hg : ContMDiff I' I'' n g) (hf : ContMDiff I I' n f) : ContMDiff I I'' n (g ∘ f) :=
by
rw [← contMDiffOn_univ] at hf hg ⊢
exact hg.comp hf subset_preimage_univ