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This may look like a silly question but I am struck in my work with this notation in one of the papers.

What is meant by $]1,1[$ ?

KSmarts
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Rajesh_Sharma
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  • Probably old fashioned notation for an open interval: $x\in]1,1[$ if and only if $-1<x<1$. Compare with $x\in[1,1]$ if and only if $-1\leq x\leq1$. –  Jan 23 '15 at 19:35
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    Please use TeX formatting in your question because the title is unreadable (I see literally: ] 1, 1[). – Tim Jan 23 '15 at 19:47
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    Why old-fashioned? This is the standard French convention. – Yuval Filmus Jan 23 '15 at 20:24
  • See also: http://math.stackexchange.com/questions/1155799/what-does-it-mean-when-range-is-expressed-between-two – Martin Sleziak Feb 19 '15 at 11:04

1 Answers1

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$]a,b[$ is an alternative notation for the open interval that I’d denote by $(a,b)$, i.e., $\{x:a<x<b\}$. Those who use this notation also write $]a,b]$ for my $(a,b]=\{x:a<x\le b\}$ and $[a,b[$ for my $[a,b)=\{x:a\le x<b\}$. Both notations are considered standard, but the $]a,b[$ notation is not common in the U.S.; I believe that it is common in France, however.

Brian M. Scott
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