Perhaps my mind is so open that it's in danger of falling out, but when people say that that's so easy to define and then don't do so, I get really confused. I'm like, have you ever seen a dude who looks like a lady? It's a question that's bedeviled sports for a long time actually - in the 60's the Olympics required "nude parades" to check that competitors were in fact women, but obviously that had some problems. I believe they eventually settled on some sort of hormone ratio as the definition.