If four points with position vectors $\overline{\mathrm{a}},\overline{\mathrm{b}},\overline{\mathrm{c}},\overline{\mathrm{d}}$ are coplanar then $\left[\overline{\mathrm{d}}\overline{\mathrm{c}}\overline{\mathrm{a}}\right]+\left[\overline{\mathrm{b}}\overline{\mathrm{d}}\overline{\mathrm{a}}\right]+\left[\overline{\mathrm{c}}\overline{\mathrm{d}}\overline{\mathrm{a}}\right]=$

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