13 questions linked to/from Notation for intervals
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### What does $]a,b[$ mean? [duplicate]

I recently encountered the above notation for sets, and I've never encountered it before. What does it refer to?
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### Alternative interval bracket notation? [duplicate]

I am reading a computer science paper and have come across some notation that I am unfamiliar with. it says to consider functions from $\mathbb{R}^N$ to $]-\infty,\infty]$ is this the same as ...
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### Let $\alpha:\langle a,b\rangle \longrightarrow \mathbb{R}^2$ be a continuous function and injective

Let $\alpha:\langle a,b\rangle \longrightarrow \mathbb{R}^2$ be a continuous function and injective how to prove that $\alpha (\langle a,b \rangle )$ has empty interior ? Any hints would be ...
### Notation $(a,b)$ for $]a,b[$.
Is there any logic or justification for the notation $(a,b)$ to represent $]a,b[$? To me this notation is very ambiguous and confusing because it looks like a couple of numbers and not an interval. ...
Yesterday when I was solving some basic geometry problems, I was curious ( I'm still though! ) about something: Why / When do some people indicate the angle with its measure $= 90^\circ$ by adding a ...