Recently there seem to have been a lot of "prove the negative" type questions. For example, the question on Egyptians recording defeats. The poster asks, "Did X ever happen" where X is some possible event in hundreds or thousands (Egypt) of years of history. In other words, the poster is hoping someone will dig up an example/counter example.
In some cases these questions are easy because there are many obvious examples of which the poster wants, but other times the question is more difficult because it is hard or impossible to find examples. Also, sometimes the poster will phrase the question in a way that makes it difficult to answer. For example, the poster might ask "Prove that the ancient Egyptians never forged steel". So, you get into this prove-the-negative problem.
Should there be some kind of guidance about prove-the-negative questions in the help?