There seems to be a disagreement about whether or when a question about mathematics notation is on-topic. For example, see the comments in \mathbb versus \mathbf one of which claims that this particular question "has nothing to do with history of science") which got a reply saying it is "just as suitable for hsm as (say) a question about the history of the division symbol or the decimal point".

I think this is worth a discussion here; not this particular question, though, but in general.

• Am I supposed to share my opinion in the question text or as an answer? – Ben Nov 20 '17 at 15:48
• Better in an answer: that way people can mentally dissociate voting on the question with voting on your opinion. – Peter Taylor Nov 20 '17 at 16:46
• Thank you @PeterTaylor, then I will do that as soon as I have formed an opinion. – Ben Nov 20 '17 at 18:28
• There is a handful of users that consider notational questions off-topic, but it has been (for as long as I can remember), and remains (as the voting in the comments indicates), a minority opinion. – Conifold Apr 5 '18 at 22:52

I personally think the "Why was the notation [...] introduced as opposed to the notation which was formerly in use"-type or "Who introduced [this essential notation] and how did people express [the corresponding thought/...] before?"-type questions (e.g., How did mathematicians notate the empty set before $\varnothing$?) are interesting and potentially of the most significant historical context. Equally appropriate are, in my opinion, those questions which are about notation and working practice of scientists; e.g., when it comes to composing texts, like Writing Mathematical Symbols in 20th century. As opposed to the questions of the (poor) form "When was [...] introduced/first used?" which are most likely answered by "According to Jeff Miller's website, [Name] was the first to use it in [Article, Year]."; history should be more than the sole dates, at least whenever possible.