I am currently taking discrete math, and we have been learning several math symbols that we have used in our proof-writing assignments. Obviously, we have discussed the $\in$ symbol for inclusion in a set, but we have never mentioned the $\ni$ symbol to show that a set contains an element, i.e. $A\ni a$.

In several instances I have found that I could state something more concisely by using this symbol. For example, in a current homework that I am working on, I would like to say that "$R_1,R_2\ni(a,b)$", where $R_1$ and $R_2$ are equivalence relations. This is more concise than saying "$(a,b)\in R_1$ and $(a,b)\in R_2$".

However, I don't see this symbol very frequently and I would prefer to make sure that it is commonly acceptable to use this symbol even when there is another way to state something like this. Is the $\ni$ symbol commonly accepted in mathematics or is the $\in$ symbol generally preferred?