Yesterday I learned 3 more LaTeX symbols while I was reviewing a paper 😺:

• an equivalence symbol: $\equiv$ $\equiv$,
• use \xi not $\ksi$ for $\xi$,
• $\widehat{}$ for estimators (in statistics), for instance: $\widehat{\xi}$.

Also, it was a good opportunity to remind myself that when looking for a specific symbol, one can always google an approximate description of the it, or one can use Detexify an extremely helpful LaTeX handwritten symbol recognition system!