"The lecture is on the disc."
Translation:La prelego estas sur la disko.
i almost did that too..lol now im understanding the argument that there is less ambiguity in esperanto a little better =)
Because the disc is the location of the lecture (e.g. you have a DVD containing a recording of the lecture) and not the topic of the lecture.
Another example: He gave a lecture on biology (topic) vs. He gave a lecture on the stage (location).