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S		 Book VI   Proposition 28
Therefore, proportionally,
    as AD is to DC, so is AG to GF,
    as DC is to CA, so is GF to FA,
    as AC is to CB, so is AF to FE,
and further,
    as CB is to BA, so is FE to EA.

And, since it was proved that,
    as DC is to CA, so is GF to FA,
and,
    as AC is to CB, so is AF to FE,
therefore, ex aequali,
    as DC is to CB, so is GF to FE. [V.22]
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