In case (i) (E AA =E BB =E AB =-1, seeded with fibers of statistical building block composition), trimers bind to fibers independent of their building block composition, and also the interaction between the hexamer exposed at a fiber end and the new hexamer lacks any selectivity. This results in fibers with a random distribution of building blocks (Figure ) and error rates are determined solely by statistics (Figure ). As expected, there was no difference between fibers that grew from surface-bound precursors compared to those grown directly from solution-phase material.