a is equal to g f. Then I double a by adding b to it, and I keep g f single; and the K that made g double I remove and place it on the opposite side, outside of h; and I do this so as not to diminish the quantity of the sector, which is 1/8 of its whole circle. Then I take from both surfaces two equal parts, which are c d; there remains g f equal to a b. But because a triangle had first been added to the lune a, which made the lune a equal to the triangle e, as is shown on the reverse of this sheet, I shall fold the same triangle over its base, so that its point will not deviate from the movement of the point of the lesser portion, as is drawn in the margin, and then I shall have g f equal to a b. Now I shall take away the added triangle of two straight sides and one curved, which was contained by the lune a, and there will remain a simple, which is unsquarable; and I shall remove the like triangle from the lune b, and there will remain b, a squarable lune, equal to a, the unsquarable lune, being composed of two curves unequal in length and unequal in curvature; while the lune b has two sides equal in curvature and in length, which is made equal by transposing g to the opposite side. It follows that the knowledge of the lune a is made manifest by comparison with the squarable lune b. The lune a being manifest, the quantity of the part of the portion g f, which is unsquarable, is made manifest.