\widecheck{ac}The \widecheck{ac} command in LaTeX is used to place a wide check accent over the specified characters, in this case, 'ac'. This is often used in mathematical contexts to denote certain transformations or operations, such as inverse Fourier transforms or other dual operations.
Inverse Fourier transform of a function f
\widecheck{f}(\xi)Expression involving the inverse Fourier transform of g
\widecheck{g}(x) = \int e^{-2\pi i x \xi} \widehat{g}(\xi) \, d\xiInverse transform of a function h over the real line
\widecheck{h}(t) = \int_{-\infty}^{\infty} h(x) e^{2\pi i xt} \, dx