Cycle spaces: invariant projections and applications to transportation cost

The paper starts with discussion of applications of cycle spaces to transportation cost. After a short survey of the known results on cycle spaces, we turn to the study of minimal projections onto cycle spaces in the corresponding $\ell_1$-spaces. This study is naturally related to the study of invariant projections on the cycle space, which, in turn, are determined by the properties of representations of the automorphism group of the corresponding graph. The main focus is on discrete tori and Hamming graphs.