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S		 Book IV   Proposition 11
I say next that it is also equiangular.

For, since
    the circumference AB is equal to the circumference DE,
    let BCD be added to each;
therefore
    the whole circumference ABCD is equal to the whole circumference BCDE.

And
    the angle AED stands on the circumference ABCD, and the angle BAE on the circumference BCDE;
therefore
    the angle BAE is also equal to the angle AED. [III.27]
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