 Before going into math, let's look at where the alpha helix exists in the Ramachandran diagram. These of these three areas, it's going to be the area in the middle, slightly to the left, where we have the alpha helix. In fact, this is one of the reasons why Pauling and Corey were able to predict the existence of alpha helix. It's simply one of these few regions where we don't have clashes of amino acids, and it's a regular structure. So they expected that this must happen in proteins, which it did. There's a second helix here to the right that we'll come back to in a second. But friend of order would say something here. You're hopefully skilled in physics, and physics has some fundamental properties that physics is translationally variant, rotationally invariant. And I also said that if I take a molecule that takes mirror image, it should have the same properties apart from the fact that it can't, that it rotates polarized light. And yet the alpha helix here is right-handed. Why is the alpha helix always right-handed if physics should not have a built-in handedness? The reason for that has to do with this chirality of the amino acids. And now we're coming back to that. So if the individual building block has a built-in handedness, if I then build larger building blocks from that fundamental building block, this handedness is going to stay built in. So there is actually occasionally a left-handed helix. You can see it's so rare that I don't think I've ever used it in any practical structure site I've looked at. So to first approximation, let's forget about it. But so when we say alpha helix, we always refer to this right-handed helix.