Equal triangles which are on equal bases, and on the same side, are also between the same parallels.Let $ABC$ and $CDE$ be equal triangles on the equal bases $BC$ and $CE$ (respectively), and on the same side (of $BE$). I say that they are also between the same parallels.For let $AD$ have been joined. I say that $AD$ is parallel to $BE$.   <prf> Thus, $AD$ is parallel to $BE$.Thus, equal triangles which are on equal bases, and on the same side, are also between the same parallels.