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It is shown in this paper by Crick that when
-helices of the same sense pack together they will probably do so about 20° away from parallel. For very long chains this may lead to a coiled-coil. The two simplest models - the two-strand rope and the three-strand rope - are described, and used to illustrate the diffraction theory already developed. It is shown that they would give a diffuse
-pattern. Possible examples of these models are briefly discussed.
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