# Is it possible to prevent substitution in approach0?

I don't know if the question is well suited here, but I don't know about a forum dedicated to this search engine, yet since it is widely used by MSE members, I guess that should do it (please redirect me, if not).

One of the main advantage of Approach0 is its internal substitution mechanism, so for instance if you search for $$f(x,y)$$ it will also search for $$f(u,v)$$ or $$f(a,b)$$, etc... bringing results that would not have appeared else, which in general is a good thing.

But in some cases, I have found it to be inconvenient, especially when you search for a specific subject.

For instance, it is good for $$i$$ to be replaced by $$n,k,j$$ and so on when the subject is about integer algebra, but I would like it not being substituted when it is the complex $$i^2=-1$$.

The same goes for $$z$$ complex, I don't want it to be substituted by $$x$$ and get all inappropriate answers only valid in the real case.

Most of the time, I workaround it by adding keywords in the search (like complex, integer, etc...) but it is not always efficient.

Is there a way to force a literal expression search in Approach0 ? Like escaping characters of some sort ?

Edit:

Thanks to Martin Sleziak, effectively the links provided shows a discussion between Wei Zhong and Jykri Lahtonen addressing this very subject.

Here is the quote by W.Z:

But I do agree it may be beneficial to give options to control what level of substitution strictness a specific query wants to apply, although technically possible, my preference is still let search engine work on its side to prioritize better matches at the same time allow more possibilities in results to improve search recall.

• Chatroom In the search of a question might be a resource, as the description says "When you are looking for a specific question (using Approach0 or by other means)". Jan 27 at 17:44
• I vaguely remember some mentions that Approach Zero gives higher priority to exact matches in the search result, see this comment or or this message. Anyway, Wei Zhong will be able to say more about this. Jan 27 at 19:57
• Thank you, it pretty much answers my question. I put an addendum above.
– zwim
Jan 27 at 20:26

Currently it is not possible. However, exact symbol matches are supposed to be prioritized to the very top of search results.

As a result, in your complex number example, it should first list as many $$i^2 = -1$$ as possible before other possibilities such as $$n^2 = -1$$. However, this gets tricky when you enter a larger expression as query where only small part of that expression is supposed to be exact match. For example, if your query is $$z=x+yi$$ but results like $$z=x+ya$$ can show up at a higher rank than say $$c=a+bi$$ simply because search engine does not have enough math semantic knowledge to preserve the meaning of imaginary letter i, rather than basic knowledge about syntax structure and a few commutative operators. In this case, I think we do need to invent a "query language" to specify those symbols you do not want to be replaced. Some thing like z = x + y \exact{i} would be desirable. So I agree this is needed.

BTW. What I plan to implement next is also related to query language. I want to add boolean filters to keywords, so that you may be able to query NOT:$z = x + y \exact{i}$ to exclude any result matches z = x + y \exact{i}. I will be investing some time to come up a way to implement these. To get it right and giving my own time constraints, please allow at least a couple of months before I can let this happen.

Thanks for your suggestion. (I have kept this idea in the project TODO list)

• This would be very helpful, indeed! Not sure we can collectively make it worth your while, but have you set up a PayPal account for tokens of appreciation? Jan 28 at 14:21
• Thanks for the answer, and also for all your efforts in making this search engine very valuable.
– zwim
Jan 28 at 14:43
• @JyrkiLahtonen Thanks for asking. Only Github sponsorship is accepted for now. The project is related to my research, so no worry I feel it is a good investment for doing it. The only issue is it may take a while for me to figure it out. Jan 31 at 10:30
• @zwim Thanks, you are welcome! Jan 31 at 10:31