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This question already has an answer here:

When I type Sum into Mathematica, it also offers Sum` in the autocomplete dropdown, but when I click the little menu button next to Sum` it doesn't take me to any help page. I was hoping this was how to create symbolic sums for manipulation, but when I tried to use it, it turned the text Sum red (instead of the usual black for recognized functions), and I had to restart the kernel before things worked again.

I've read questions such as Meaning of backtick in floating-point literal, but I can't find any reference to how the backtick is used with functions.

What is the meaning of Sum` or what is the help file that explains it?

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marked as duplicate by Mr.Wizard Feb 6 '17 at 18:13

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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To elaborate a bit on Michael's comment, let's first consider this statement from the docs:

Sum and Product use over 100 pages of Wolfram Language code.

Executing ?Sum`* will in fact show you some of the internal routines used behind the scenes by the function Sum[]. You, the regular user, are not usually intended to access these by yourself; however, if you look at the names of some of these, you'll see some correspondence with the list of Methods supported by Sum[].

So, for instance,

Sum[i^2, i, Method -> "Polynomial"]

will at some point call

Sum`SumPolynomialFunction[i^2, i]

P.S. there is also a Product` context.

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