Latex的各种帽子

\hat{A}

\widehat{A}

\tilde{A}

\widetilde{A}

\overline{A}

\underline{A}

\overbrace{A}

\underbrace{A}

\overset{a}{b}

\underset{a}{b}

\overleftarrow{A}

\overrightarrow{A}

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