Hey, here's a quote from that thread I just mentioned, by none other than Amos:

"For a large system such as a nation, a negative proposition pretty well leads to an unbounded set of test cases (infinite proving required to be conclusive). In general a negative requirement involves a huge number of possible conditions in which 'the system under consideration is NOT doing X' that it becomes practically impossible."

In other words, a logical proof that bagpipes did not exist in BC Ireland is impossible. However, a proof that they DID exist would be easy...if only there were some evidence!