# Talk:Urysohn's Lemma

Was the recent change from $U_p^-$ to ${U_p}^-$ done because it looked like $U_{p^-}$ or for some other reason? Because this seems to be a downright MathJax rendering bug. — Lord_Farin (talk) 15:29, 8 September 2015 (UTC)

- Yes, that is why. It makes logical sense as well: you want to denote the closure of $U_p$ and not underscore with $p$ the set $U^-$. Even if they fix the bug, it will still work well as it is rendered.

- I have taken to use a similar technique for stuff like $x_2^2$ where if you do ${x_2}^2$ it's more obvious what it means. --prime mover (talk) 16:44, 8 September 2015 (UTC)

- FYI: It is known. See here.— Lord_Farin (talk) 17:24, 8 September 2015 (UTC)

- Do we need that workround? I'd say not -- I'd rather we put curlies round the argument as we find them. --prime mover (talk) 17:56, 8 September 2015 (UTC)

## My alternative proof attempt

In this PDF file I present an alternative proof of Urysohn's Lemma (using my theory of funcoids). However my proof is conditional (relies on this unproved conjecture).

## Possible typo in a formula

I suspect \(x \in U_r^- \implies \forall x > r: x \in U_s\) (in proof of (a)) should instead be \(x \in U_r^- \implies \forall s > r: x \in U_s\).

Or what is \(s\) otherwise? --VictorPorton (talk) 17:37, 21 July 2016 (UTC)

- Corrected --VictorPorton (talk) 13:17, 22 July 2016 (UTC)

- Thank you for attending to these issues. --prime mover (talk) 16:50, 22 July 2016 (UTC)

## Possible another math typo

"let \((c..d)\) be an open real interval containing \(f(x)\)." should probably instead be "let \((c..d)\) be an open real interval containing \(f(x_0)\)."

- Feel free to compare it closely with the source on PlanetMath where it came from. You may well be right.

- Incidentally, we don't use the math ... /math delimiters here, we use dollar-sign delimiters exclusively for important technical reasons which unfortunately do not admit exceptions. --prime mover (talk) 19:10, 21 July 2016 (UTC)