isotopy doesn't make sense (Milnor)

Question

hello,

I am having a hard time following this isotopy put forth by Milnor in On the Total Curvature of Knots

For each $c$ and $p$ in $\mathbb{R}^{n-1}$ such that $\|c-p\| > < r$, there is an isotopy, $f_u^{c\; > p} (\gamma), 0 \le u \le 1$, of $\mathbb{R}^{n-1}$ onto itself which transforms $c$ into $p$ and leaves fixed all points of $\mathbb{R}^{n-1}$ outside the $(n-2)$-sphere of radius $r$

This concept makes sense, but the paper continues saying:

For example,

$f_u^{c\; p}(\gamma) = \gamma - u ( 1 - \frac{\|\gamma - c\|}{r} )(p -c)$ for $\|\gamma - c\| \le r$

$f_u^{c\; p}(\gamma) = \gamma$ for $\|\gamma - c\| \ge r$

If you plug the value $\gamma = c$ into this where $u = 1$, you get

$c - (1)(1)(p-c) = 2c - p$

I thought the idea was to transform c into p?

It seems weird that you have the vector $p-c$ with some appropriate magnitude being subtracted instead of added.

Any thoughts on this would be really helpful,

Thanks

Answer 1

[I'm entering my comment above as an answer here, so as to stop this question being bumped to the front page in the future.]

There is simply a typo: the definition of $f_u^{cp}(\gamma)$ should be $\gamma + u$(etc. ...).