Mathematical formulas are typeset in $$italics\text{.}$$
For some important mathematical structures we use a character set called black board bold, in particular we use $$\mathbb{A}\text{,}$$ $$\mathbb{N}\text{,}$$ $$\mathbb{P}\text{,}$$ $$\mathbb{W}\text{,}$$ and $$\mathbb{Z}\text{.}$$
While variables are typeset in $$italics$$ we typeset characters and text that we manipulate in courier (the typeface of most mechanical typewriters).