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03:11
@MartinSleziak Thank you for posting this, I do know other sites that search MSE, but I do tried a query on searchOnMath website: searchonmath.com/…
It seems they do not index MSE but instead include Socratic, mathworld of wolfram, planetmath, but mostly Wiki pages.
Although not searching MSE, users may also find it useful when other means fail to find good result.
 
2 hours later…
05:46
SearchOnMath and uniquation are mentioned here: Is there any third party search engine for MathOverflow?
It seems that uniquation no longer exists.
When trying SearchOnMath, I did not get results from math.SE - same sa you.
They do not explicitly say in About Us what they use as sources:
> SearchOnMath currently performs its search on several bases of mathematical knowledge available on the Internet. ... If you own a web site containing mathematical formulas, please contact us. We're always looking for new knowledge to incorporate into our database.

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