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the parallelogram BDLM is double of the triangle ABD,
for they have the same base BD and are in the same parallels BD, AL. [I.41]
And
the square GB is double of the triangle FBC,
for they have the same base FB and are in the same parallels FB, GC. [I.41]
[But the doubles of equals are equal to one another.]
Therefore
the parallelogram BL is also equal to the square GB.
