#### 16.2.1 Arrows

These are the arrows that come with standard LaTeX. The latexsym and amsfonts packages contain many more.

SymbolCommand
\Downarrow
\downarrow
\hookleftarrow
\hookrightarrow
\leftarrow
\Leftarrow
\Leftrightarrow
\leftrightarrow
\longleftarrow
\Longleftarrow
\longleftrightarrow
\Longleftrightarrow
\longmapsto
\Longrightarrow
\longrightarrow
\mapsto
\nearrow
\nwarrow
\Rightarrow
\rightarrow, or \to
\searrow
\swarrow
\uparrow
\Uparrow
\updownarrow
\Updownarrow

An example of the difference between \to and \mapsto is: $$f\colon D\to C$$ given by $$n\mapsto n^2$$.

For commutative diagrams there are a number of packages, including tikz-cd and amscd.