Example 4

Tag 082W, permanent. Cite it as [Bourbaki, Tag 082W].

Functions of a Real Variable, chapter I, § 1. FIRST DERIVATIVE

The scalar function $|x|$ , defined on $\mathbf{R}$ , has right derivative $+1$ and left derivative $-1$ at $x = 0$ ; it is not differentiable at this point.

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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