Latex各种箭号符号，以及在箭头上方添加字母等符号的方法

\uparrow	$\uparrow$
\downarrow	$\downarrow$
\Uparrow	$\Uparrow$
\Downarrow	$\Downarrow$
\updownarrow	$\updownarrow$
\Updownarrow	$\Updownarrow$
\rightarrow	$\to$
\leftarrow	$\leftarrow$
\Rightarrow	$\Rightarrow$
\Leftarrow	$\Leftarrow$
\leftrightarrow	$\leftrightarrow$
\Leftrightarrow	$\iff$
\longrightarrow	$⟶$
\longleftarrow	$⟵$
\Longrightarrow	$⟹$
\Longleftarrow	$⟸$
\mapsto	$\mapsto$
\longmapsto	$⟼$
\hookleftarrow	$\hookleftarrow$
\hookrightarrow	$\hookrightarrow$
\leftharpoonup	$\leftharpoonup$
\rightharpoonup	$\rightharpoonup$
\leftharpoondown	$\leftharpoondown$
\rightharpoondown	$\rightharpoondown$
\rightleftharpoons	$\rightleftharpoons$
\leadsto	$⇝$
\nearrow	$\nearrow$
\searrow	$\searrow$
\swarrow	$\swarrow$
\nwarrow	$\nwarrow$
\nleftarrow	$\nleftarrow$
\nrightarrow	$\nrightarrow$
\nLeftarrow	$\nLeftarrow$
\nRightarrow	$\nRightarrow$
\nleftrightarrow	$\nleftrightarrow$
\nLeftrightarrow	$\nLeftrightarrow$
\dashrightarrow	$⇢$
\dashleftarrow	$⇠$
\leftleftarrows	$\leftleftarrows$
\leftrightarrows	$\leftrightarrows$
\Lleftarrow	$\Lleftarrow$
\twoheadleftarrow	$\twoheadleftarrow$
\leftarrowtail	$\leftarrowtail$
\looparrowleft	$\looparrowleft$
\leftrightharpoons	$\leftrightharpoons$
\curvearrowleft	$\curvearrowleft$
\circlearrowleft	$\circlearrowleft$
\Lsh	$\Lsh$
\upharpoonleft	$\upharpoonleft$
\downharpoonleft	$\downharpoonleft$
\upuparrows	$\upuparrows$
\multimap	$⊸$
\leftrightsquigarrow	$\leftrightsquigarrow$
\rightrightarrows	$\rightrightarrows$
\rightleftarrows	$\rightleftarrows$
\twoheadrightarrow	$\twoheadrightarrow$
\rightarrowtail	$\rightarrowtail$
\looparrowright	$\looparrowright$
\rightleftharpoons	$\rightleftharpoons$
\curvearrowright	$\curvearrowright$
\circlearrowright	$\circlearrowright$
\Rsh	$\Rsh$
\downdownarrows	$\downdownarrows$
\upharpoonright	$\upharpoonright$
\downharpoonright	$\downharpoonright$
\rightsquigarrow	$⇝$