Arrows

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

Symbol	Command
⇓	\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.