latex 显示效果
\uparrow
\downarrow
\Uparrow
\Downarrow
\updownarrow
\Updownarrow
\rightarrow
\leftarrow
\Rightarrow
\Leftarrow
\leftrightarrow
\Leftrightarrow
\longrightarrow
\longleftarrow
\Longrightarrow
\Longleftarrow
\longleftrightarrow
\Longleftrightarrow
\mapsto
\longmapsto
\hookleftarrow
\hookrightarrow
\leftharpoonup
\rightharpoonup
\leftharpoondown
\rightharpoondown
\rightleftharpoons
\leadsto
\nearrow
\searrow
\swarrow
\nwarrow
\nleftarrow
\nrightarrow
\nLeftarrow
\nRightarrow
\nleftrightarrow
\nLeftrightarrow
\dashrightarrow
\dashleftarrow
\leftleftarrows
\leftrightarrows
\Lleftarrow
\twoheadleftarrow
\leftarrowtail
\looparrowleft
\leftrightharpoons
\curvearrowleft
\circlearrowleft
\Lsh
\upuparrows
\upharpoonleft
\downharpoonleft
\multimap
\leftrightsquigarrow
\rightrightarrows
\rightleftarrows
\rightrightarrows
\rightleftarrows
\twoheadrightarrow
\rightarrowtail
\looparrowright
\rightleftharpoons
\curvearrowright
\circlearrowright
\Rsh
\downdownarrows
\upharpoonright
\downharpoonright
\rightsquigarrow