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    \pscircle(0,0){2}
    \SpecialCoor
    \psarc[linecolor=red,linewidth=2pt]{-}(0,0){2}{-45}{45}
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    \uput[r](2;45){$A \; \frac{\pi}{4}$}
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    \uput[r](2;-45){$B \; \frac{-\pi}{4}$}
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