Appendix. Math symbols and commands | LaTeX manual

1. Lowercase Greek letters

There’s no \omicron, since it looks the same as o.

2. Uppercase Greek letters

The other Greek capitals appear in the roman alphabet (\Alpha={\rm A}, \Beta={\rm B}, etc.).

3. Miscellaneous symbols of type Ord

4. Large operators

5. Binary operations

6. Relations

7. Relations

8. Arrows

9. Openings

10. Closings

11. Alternate names

There’s also \iff, which is just like \Longleftrightarrow except that it puts an extra thick space at each side.