# Database for mathematical syntax

I sometimes encounter strange mathematical syntax like ${}_n\complement_k$ for $n\choose k$, or $x^{\bar k}$ which is defined as $\Gamma(x+k)/\Gamma(x)$.

Is there any good resource where one can look for mathematical syntax and get a brief explanation? (Except asking on math.SE, of course :).

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There's this and this... –  Guess who it is. Sep 13 '11 at 18:09
Notations are usually defined when first given, and one sort of gathers along his own database. It can be hard when $\overline A$ is used for so many things in so many contexts. –  Asaf Karagila Sep 13 '11 at 18:40
I've thought about this myself, and even considered putting together my own electronic symbol reference but, like Asaf notes, not only is mathematical notation polymorphic, but it also varies from author to author and discipline to discipline. Sure, you could provide a one-to-many lookup but without context I'm not sure how helpful it would be. –  ItsNotObvious Sep 13 '11 at 20:22
@3Sphere Such a reference is quite useful if you see a formula in the Internet or in a paper where the author sees no reason to include a syntax definition. So even a lookup with many definitions is great, as one can often tell the right one from the context. –  FUZxxl Sep 13 '11 at 20:39
"in a paper where the author sees no reason to include a syntax definition." - one way around that is to look at the paper's references, which hopefully might be a bit more forthcoming with explaining the notation... –  Guess who it is. Sep 13 '11 at 23:54