The selection of fonts within math mode is quite different to that of text fonts.
Some math fonts are selected explicitly by one-argument commands such
as \mathsf{max} or \mathbf{vec}: these are called math
alphabets. These math alphabet commands affect only the font used
for letters and symbols of type \mathalpha (see
Section 3.6); other symbols within the argument
will be left unchanged. The predefined math alphabets are:
Other math fonts are selected implicitly by TeX for symbols, with
commands such as \oplus (producing 
) or with straight
characters like >> or +. Fonts containing such math symbols are
called math symbol fonts. The predefined math symbol fonts
are:
Some math fonts are both math alphabets and math symbol
fonts, for example \mathrm and operators are the same font, and
\mathnormal and letters are the same font.
Math fonts in LaTeX have the same five attributes as text fonts:
encoding, family, series, shape and size. However, there are no
commands that allow the attributes to be individually changed.
Instead,
the conversion from math fonts to these five attributes is controlled
by the math version. For example, the normal math version
maps:
The bold math version is similar except that it contains bold fonts.
The command \boldmath selects the bold math version.
Math versions can only be changed outside of math mode.
The two predefined math versions are:
Packages may define new math alphabets, math symbol fonts, and math versions. This section describes the commands for writing such packages.