bad: $(\forall x,y\in A) x\cdot y = y \cdot x$; correct: $(\forall x,y\in A)(x\cdot y = y \cdot x)$
Presentation
Example of presentation done in BEAMER: prezentacjaJCI.zip (it is in polish)
Example: my presentation from SODA'17 conference: NonPlaneTreesJCI.pdf and compressed files: Referat.zip. I had about 15 minutes for this presentation at the SODA'17 conference held in Barcelona on January 16-19.