 So if we look at those four helix bundles to start with, here is one example. Here's a second example and here is a third example. They are seemingly similar, but you would probably say that that one is reasonably ordered, that one is reasonably ordered and this one is a horrible mess. There is a reason for the horrible mess, so let's wait for that a second. This four helix bundles is something that occurs in cytochrome C domains. This is part of something called T and V that I won't tell you what it is quite, and this is a hem erythrin. All these are anti-parallel. I haven't talked to you yet about anti-parallel versus parallel when it comes to helices, but anti-parallel with helices just means that I have one helix going up here and then I have a loop and then a helix going down and then a loop and then a helix going up and then a loop and then a helix going down. If I had to create, it's very rare with parallel alpha helices because then again I would need some other structure. That should then be another helix, but if that helix is in contact with these, then it is an anti-parallel structure, so I can really only have parallel helices when it's mixed helix and sheet, which I'm not going to talk about quite yet.