Wikipedia:Reference desk/Archives/Mathematics/2017 December 28

= December 28 =

Untitled question
Hi. I am considering the infinite strip $$(x,y): 0\leq y\leq 1$$ but with $$(x,0)$$ identified with $$(-x,1)$$. Is there a word for this space? It is not a Klein bottle, but it's not orientable so it's not an (infinite) cylinder either. Anyone? Robinh (talk) 22:14, 28 December 2017 (UTC)


 * It's just a Möbius strip with the boundary removed (in this case, the boundary is just one copy of a circle). –Deacon Vorbis (carbon &bull; videos) 23:38, 28 December 2017 (UTC)
 * thanks for this. It's obvious now you've pointed it out.  If this is the best description, happy to mark as .  Thanks, Robinh (talk) 23:52, 28 December 2017 (UTC)

When did the last country switch to Western-looking numerals?
Or at least start using them more than 50% of the time. Officially switching isn't that important if the proclamation's usually ignored after all. Or is the question mistaken and there are countries where other numerals are used more than Western-style? Sagittarian Milky Way (talk) 22:50, 28 December 2017 (UTC)


 * According to Eastern Arabic numerals, those numerals (and not the "Western-looking" ones) are still used in large parts of the Arabic-speaking world and some nearby countries.


 * This doesn't mean the question doesn't make sense: we can still talk about countries that have switched in the past and which one was the most recent. I would not be surprised if the answer was Turkey, which switched its alphabet from the Arabic one to a Latin-based one starting in the 1920s, but I don't know what numerals they used before the switch. --76.69.117.217 (talk) 04:01, 29 December 2017 (UTC)


 * It appears to me that using different numerals in different contexts is quite common, so there's not really a date you can point to where a country switched to a new system. Instead it's more a slow process taking place over a long period of time, and saying one country switched before another is rather meaningless. In Western Europe, for example, which adopted Arabic numerals for the most part centuries ago, people still use Roman numerals on occasion. --RDBury (talk) 12:25, 29 December 2017 (UTC)


 * This essay, Will Burmese numerals ever fall out of fashion?, on the persistence of Burmese numerals may help guide your research. -- ToE 16:32, 29 December 2017 (UTC)


 * Is the question limited to all numerals? In Chinese, the zero (零) is a bit of a pain. So, most people have adopted 0 instead. They still use 一 二 三 ... for everything else. They also use multipliers like 十 and 百 where we've dropped them in writing even though we still say them, even if we've abbreviated "four-ten two" to "forty two". 71.85.51.150 (talk) 03:40, 30 December 2017 (UTC)
 * These characters are more like our words for numbers than our numerals, and Western Arabic numerals are quite common in China today. Certainly all arithmetic is done today with Western Arabic numerals there, so it's nothing like the continued usage of Eastern Arabic numerals in the Mashriq. Double sharp (talk) 03:43, 30 December 2017 (UTC)
 * Arabic numerals are commonly used in China in most of the places they are used in the English speaking countries. For prices, dates, sizes, phone numbers. Number characters tend to be only used in more formal contexts, and when numbers occur as words or parts of words such as 四川. As for 十 and 百 they occur mostly in speech, much like "forty", "one hundred" do in English, when e.g. reading out numbers. But as in English when writing numbers they are normally omitted.-- JohnBlackburne wordsdeeds 10:14, 30 December 2017 (UTC)