##  Class files

In mathematical mode you can change the typefaces of the fonts when needed. For instance, it's customary to represent real numbers with a blackboard bold font, or topological spaces with calligraphic font. This article shows several fonts in math mode. Contents 1 Introduction 2 Capital letters-only font typefaces 3 Other mathematical fonts 4 Further reading  Introduction For some elements is convenient to have the possibility of changing the font typeface. Let $$\mathcal{T}$$ be a topological space, a basis is defined as $\mathcal{B} = \{B_{\alpha} \in \mathcal{T}\, |\, U = \bigcup B_{\alpha} \forall U \in \mathcal{T} \}$ Several fonts require to add the line \usepackage{amssymb} to the preamble to work.   Open an example in ShareLaTeX  Capital letters-only font typefaces There are some font typefaces that support a limited number of characters, these fonts usually denote some special sets. \begin{align*} RQSZ \\ \mathcal{RQSZ} \\ \mathfrak{RQSZ} \\ \mathbb{RQSZ} \end{align*} This example shows Calligraphic, Fraktur and Blackboard bold typefaces. For instance, to display the R in blackboard bold typeface \mathbb{R} will do the trick.   Open an example in ShareLaTeX  Other mathematical fonts It's possible to set a different font family for a complete mathematical expression. \begin{align*} 3x^2 \in R \subset Q \\ \mathnormal{3x^2 \in R \subset Q} \\ \mathrm{3x^2 \in R \subset Q} \\ \mathit{3x^2 \in R \subset Q} \\ \mathbf{3x^2 \in R \subset Q} \\ \mathsf{3x^2 \in R \subset Q} \\ \mathtt{3x^2 \in R \subset Q} \end{align*} In this cases not only letters but all characters change its appearance, for example \mathit{3x^2} displays the equation italicised.   Open an example in ShareLaTeX  Further reading For more information see Mathematical expressions Subscripts and superscripts Bold, italics and underlining Font sizes, families, and styles Font typefaces Text alignment The not so short introduction to LaTeX2ε