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On Milnor's Morse theory, we have:

Given a manifold $M\subset\mathbb{R}^n$, let $N=\{(q,v)~\vert~ q\in M,$ $v$ is perpendicular to $M$ at $q\}\subset M\times \mathbb{R}^n$

And $E:(q,v)\mapsto q+v$.

A point $e\in \mathbb{R}^n$ is a focal point of a manifold $M\subset \mathbb{R}^n$ if $e=q+v$ for some $(q,v)\in N$ and the Jacobian of $E$ at $(q,v)$ has nullity $>0$.

My question is, Milnor claims that a focal point of M is a point in $\mathbb{R}^n$ where nearby normals intersect, how to see this claim?

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