For let the solids AO, GP be completed.
Since the parallelogram AF is double of the triangle GHK, while the parallelogram HK is also double of the triangle GHK, [I. 34] therefore the parallelogram AF is equal to the parallelogram HK.
But parallelepipedal solids which are on equal bases and of the same height are equal to one another; [XI. 31]
therefore the solid AO is equal to the solid GP.
And the prism ABCDEF is half of the solid AO, and the prism GHKLMN is half of the solid GP; [XI. 28]
therefore the prism ABCDEF is equal to the prism GHKLMN.