Figure1: The full number of arrangements that can be generated from a protein composed of 3 beta-strands when right handed crossover of the beta-strands is included: (a) no crossover, (b) all crossovers and (c) a mixture of (a) and (b). The notation below indicates the location of the next strand (±1, ±2) and the x (±1x, ±2x) indicates a crossover beta-strand (Richardson, 1977). The total number of arrangements follows the rule 2n-1n!/2 (Cohen et al., 1982), where n is the number of beta-strands.