Meaning of $\rightarrow$ I've come across this:
$$b_H=\frac{\sum_{i=1}^n b_ig_{(i\rightarrow H)}}{\sum_{i=1}^n g_{(i\rightarrow H)}}$$
and I'm wondering what the $i\rightarrow H$ part especially means.
This formula is used when calculating the value of a criterion from a set of weighted sub-criteria. Here's an example:
criterion                | weight(g) | rating(b)


*

*Base criterion       |     | 3.17


*

*criterion A      |  1  | 3.66


*

*criterion 1  |  1  | 3

*criterion 2  |  2  | 4


*criterion B      |  3  | 3


*

*criterion 3  |  1  | 2

*criterion 4  |  3  | 2

*criterion 5  |  4  | 4
As you can see criterion A is calculated from criterion 1 and 2, B from 3 to 5 and then the base criterion from A and B.
From my searches on the internet I've found that it has something to do with domains and co-domains. But I can't make sense of it in this context since $i$ always refers to the same criterion and I'm not using the value of a parent weight, if that makes sense? Googling "rightarrow math" spits out a lot of totally unrelated nonesense, so my apologies if this has been asked before.
I hope it makes sense what I'm trying to understand (last time I've seen this was back in school with $\lim_{x\to 0}$ which was a long time ago and it seems to be used differently here) and that somebody can explain this to me.
Thank you very much!
 A: It seems that H stands for any particular criterion that is made up of subcriteria, so in this case A, B, or the base. The formula tells you that you have to take the weighted average rating of those subcriteria to get the rating of H. Presumably they intend it to mean that there is a mapping from the indices $1$ to $n$ to the subcriteria of $H$, and the subscript $(i \rightarrow H)$ means the $i$th subcriterion of $H$.
It is very sloppy of them to leave things undefined and use a strange non-standard notation. Very odd also that they didn't use the notation in the subscript for b. 
I would probably use set notation for it:
$$b_H = \frac{\sum_{h \in H} b_hg_h}{\sum_{h \in H} g_h}$$
and explain that $h \in H$ means that the sum goes over all criteria $h$ that are direct subcriteria of $H$. This is also a slight abuse of notation in that it overloads $H$ to mean a criterion as well as the set of its subcriteria.
Alternatively you could use:
$$b_H = \frac{\sum_{i=1}^n b_{h_i}g_{h_i} }{ \sum_{i=1}^n g_{h_i}}$$
and explain separately that $h_1, h_2, ..., h_n$ are the subcriteria of $H$.
