 So to complete the statistics on amino acid occurrence, let's look at that C-alpha-C-beta bond again. Again, you see here that there's a systematic pattern where the bond is pointing... The first bond out from the alpha helix is always pointing towards the N-terminus. This will lead to many systematic differences I already mentioned, in particular that it's going to be easier for things to snorkel out from the N-terminus, but it's also going to be easier to snorkel in from the C-terminus. You don't necessarily have to believe me there. There's a lot of statistics we've been able to do with PDB structures, just calculating average sequences. You can also calculate average occurrences, where in a helix do things tend to occur? Do they occur in an N-terminus or a C-terminus? And this pretty much spears out. So this is not just based on simple models, but a ton of statistics from the protein data bank.