The first step in this direction was taken by Zubarev et al. who constructed a superset of carbon fixation cycles using a small set of reaction rules applied to acetate, H2O, CO2, and H2. This exploration rediscovered the rTCA cycle, but more surprisingly it also revealed a large set of parallel and partially overlapping fixation cycles (i.e., sharing some reactions with the rTCA cycle but many independent) that are also thermodynamically favorable. This clarified that many thermodynamically favorable CO2 fixation cycles could exist provided that H2 is available as a reductant but still left unaddressed the central question of whether any of these alternatives are kinetically relevant.