A lipogram is a text where one or more letters have been omitted on purpose. A great example is French author George Perec’s novel La disparition, which doesn’t even once contain the letter E.
In an Esperanto lipogram – which letter would be ”hardest” to avoid? The resulting text should still be fairly easy to understand – although a bit of quirkiness would be okay! :-) (Such as writing Esperant’ with an ellipsis, for example. Perec’s novel, which I read in an English translation [also without any E!], is certainly full of quirky rewordings…)