If then the square on HF is greater than the square on FK by the square on a straight line commensurable with HF, while the annex FK is commensurable in length with the rational straight line FG set out, KH is a second apotome. [X. Deff. III. 2]
But FG is rational;
so that the “side” of LH, that is, of EC, is a first apotome of a medial straight line. [X. 92]