English
If b ≠ a, then differentiability within at dslope f a, s, b is equivalent to differentiability within f at b.
Русский
Если b ≠ a, дифференцируемость dslope f a на s в точке b эквивалентна дифференцируемости f на s в точке b.
LaTeX
$$$\text{DifferentiableWithinAt}( dslope\ f\ a, s, b) \iff \text{DifferentiableWithinAt}( f, s, b) \quad (b \neq a)$$$
Lean4
theorem of_dslope (h : DifferentiableAt 𝕜 (dslope f a) b) : DifferentiableAt 𝕜 f b :=
differentiableWithinAt_univ.1 h.differentiableWithinAt.of_dslope