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It could be a misprint or typo in what I'm reading, but I just want to make sure.

I'm reading Loring Tu's "An Introduction to Manifolds", and at the end of the first chapter, one of the problem states:

$\textbf{1.3 A diffeomorphism of an open interval with}\,\,\mathbb{R}$

Let $U\subset\mathbb{R}^n$ and $V\subset\mathbb{R}^n$. A $C^\infty$ map $F: U\rightarrow V$ is called a diffeomorphism if it is bijective and has a $C^\infty$ inverse $F^{-1}:V\rightarrow U$.

(a) Show that the function $f: \,\,\,]-\pi/2, \pi/2[\rightarrow \mathbb{R}, f(x)=\tan(x)$ is a diffeomorphism.

To be clear, I'm not asking for help with the problem, just the notation he uses. Elsewhere in the text, it appears that every time he mentions an open interval, he uses this $]a,b[$ notation, but for closed intervals he uses the traditional $[a,b]$.

Is this notation commonly used, or likely some sort of misprint with the pdf I'm reading from?

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    $\begingroup$ At some places in the world it is the standard notation for open intervals. $\endgroup$ – quid♦ May 31 at 14:19
  • $\begingroup$ Could you point me to more info about it? This sort of thing seemed difficult to search for when I tried $\endgroup$ – Calvin Godfrey May 31 at 14:19
  • $\begingroup$ There is really nothing more to it that and inverted bracket is used instead of a parenthesis. I am pretty sure the question is a duplicate which is why I did not answer it. $\endgroup$ – quid♦ May 31 at 14:20
  • $\begingroup$ You're welcome to close it or delete it, then! $\endgroup$ – Calvin Godfrey May 31 at 14:21

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