# How to search for a formula/expression

Suppose I want to search for instances where an expression similar to $x_n^2-x_{n-1}x_{n+1}$ shows up. How would I do that?

I suppose the question goes beyond searching MSE. Are there search engines which handle math formulas in a particularly effective way?

Edit: I am listing some leads in the comments which I found useful:

Uniquation, a mathematical formula search engine. And here is the response to my query above. Perhaps this can be an option on MSE.

• – Martin Sleziak Jul 4 '13 at 14:42
• symbolab.com is another one. – Peter Krautzberger Jul 5 '13 at 17:29
• @PeterKrautzberger Thanks, but when I tried above query on it I could not see a connection between reply and query. Also it is not LaTeX based. Perhaps I am mistaken. Symbolab – Maesumi Jul 6 '13 at 0:16
• Doesn't the math.se search engine match against the raw latex in the posts? – Jack M Jul 9 '13 at 16:12
• @JackM if you are searching for $a^2+b^2=c^2$ the Uniquation seems to also get you $x^2+y^2=z^2$ and the equivalents. So searching a formula becomes a tricky search for a concept. – Maesumi Jul 9 '13 at 21:18
• Another related question at MO: mathoverflow.net/questions/162487/… – Martin Sleziak Apr 6 '14 at 6:45

See my side-project, it is an open-source math-aware similarity search engine.

http://approach0.xyz

I am hoping someone interested can join and form a community to push this project forward, this is the reason I am posting here.

searchOnMath looks interesting too. I think you can do what you want

Feb. 2019 Update from one the developers Flavio Gonzaga:

Recently our tool has indexed both: Mathematics and MathOverflow.

Currently, SearchOnMath is the mathematical search engine with the largest number of indexed sites (including Wikipedia, Wolfram MathWorld, among others ...).

P.S.: please, enclose formulas between \${}\$. e.g. \${x+y}\$.

The following Youtube video illustrates how it works: SearchOnMath - a brief guide

We’d love to hear your feedback.

• Is there a search that when you look for $x^y=y^x$ it provides articles with equivalent equations that can be obtained by simple substitutions, such as $a^b=b^a$. That is a search engine that understands the concept of equation beyond just appearance of letters. SearchOnMath is a valuable tool but I do not think it searches for equivalent equations. – Maesumi May 30 '15 at 21:07
• According to a recent announcement on Mathematics Meta, SearchOnMath now indexes MathOverflow and Mathematics Stack Exchange. – Martin Sleziak Feb 1 at 5:10