There are a very large number of special symbols and notations, too many to list here; see the short listing $\LaTeX$ and $\mathcal{A}_{\Large\mathcal{M}}\mathcal{S}$-$\LaTeX$ Symbols prepared by Dr. Emre Sermutlu, or the exhaustive listing The Comprehensive $\LaTeX$ Symbol List by Scott Pakin. Some of the most common include: More @Wikipedia
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