Latex is formatting this formula all squished together. How do I format it properly?
$\varphi' \gets \left\{ C_n \setminus C_i \middle| C_n \textrm{does not interfere with} C_i\right\}$

EDIT: Here's my solution, which produces exactly what I want. However, this spacing should be done automatically, not manually. Are there any packages that define macros for this easily?
$\varphi' \gets \{\, C_n \setminus C_i \,|\, C_n \textrm{ does not interfere with } C_i\,\}$

\text{ does not interfere with }- note the space at the beginning and end. – Werner Apr 19 '15 at 18:17\textstring or specify an explicit space such as "backslash space" or\quad. – barbara beeton Apr 21 '15 at 16:48