I need to use | with the mean of "such that". It's in an expression with fraction and so I need to have a big |. I've tried to use \displaystyle before | but it doesn't work. Putting \left before | work, but Texstudio give an error because there isn't any \right. What can I do?
If you want only a left delimiter but not a right one, you can use
\left| \right. (with a dot).