Wikipedia:Reference desk/Archives/Mathematics/2017 December 4

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December 4

Subring of prime ring

Is a subring of a non-commutative prime ring always itself a prime ring? If yes, give a proof; otherwise, give a counterexample. GeoffreyT2000 (talk) 05:51, 4 December 2017 (UTC)

This looks like homework so I'll let you work out the details, but it looks like you might want to try taking R to be the ring of 2x2 matrices over a field and D to be the subring of diagonal matrices. --RDBury (talk) 17:50, 4 December 2017 (UTC)

No LaTeX \phantom in WP? Work around?

As the title says ... I did not succeed to find something in Help:Displaying a formula and also not in other places, so I ask for cheap tricks, possibly saving me to dig into arrays with elaborate aligning. Purgy (talk) 18:08, 4 December 2017 (UTC)

No, \phantom isn't supported. What are you trying to do? For the future, this would probably be better at Help Talk:Displaying a formula or WT:WPM. –Deacon Vorbis (carbon • videos) 18:40, 4 December 2017 (UTC)

Thanks for the confirmation, and I'll tell my woes there. Sorry, for having been wrongly here. Purgy (talk) 08:53, 5 December 2017 (UTC)

Um, DV, Help talk:Displaying a formula is for discussing ways to improve the page Help:Displaying a formula; it's not a support forum. @Purgy Purgatorio: a better place to try would probably be Wikipedia:Help desk, since that's specifically set up to help users "use or edit Wikipedia". (time passes, as I start to type up a reply at Help:Displaying_a_formula…) I see that users have begun to ask you followup questions at Help talk:Displaying a formula#Work around for LaTeX \phantom?, so maybe you will end up getting some help there. Alternatively, you could just start editing whichever article you want to contribute to, and if someone reverts your changes because of problems with the TeX coding, pull the math content out of the page history, post it to the talk page, and ask for help from users who know how to edit math. Presumably, if the article calls for heavy math coding, there will be users watching the article who can do that.) - dcljr (talk) 10:28, 5 December 2017 (UTC)

@Dcljr, thank you, for your hints to the bureaucratically correct use of "Help talk:Displaying a formula", for pointing me to the universal "Wikipedia:Help desk", and for mentioning the possibility of discussing my problem on some specifically cognizant talk page. — It's just that I got simply no reply to my question referring to this at that talk page, and that I see the Help desk crowded with people not really interested and involved in math layout (as seemingly is the whole upper squad of WP). Obviously, my usurpational attack on this here Reference desk, which supplied me both with further contacts and with a confirmation of my conjecture, is at least, albeit not fully de rigeur, quite successful. Thanks for caring, anyhow. :) Purgy (talk) 19:42, 5 December 2017 (UTC)