English
If h : LineDifferentiableWithinAt 𝕜 f s x v, then for any scalar c, f is line differentiable within s at x for direction c v.
Русский
Если h : LineDifferentiableWithinAt 𝕜 f s x v, то при любом скаляре c функция f дифференцируема вдоль направления c v внутри s.
LaTeX
$$$$ HasLineDerivWithinAt 𝕜 f s x v \Rightarrow LineDifferentiableWithinAt 𝕜 f s x (c \cdot v) $$$$
Lean4
theorem smul (h : LineDifferentiableWithinAt 𝕜 f s x v) (c : 𝕜) : LineDifferentiableWithinAt 𝕜 f s x (c • v) :=
(h.hasLineDerivWithinAt.smul c).lineDifferentiableWithinAt