fact: Definition step_dist (d : K) p x := (step c p x.1 x.2, d * dest_dist x.2 / #|free_coports|%:R ).
imports: mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix perm) ssr_ext ssralg_ext fdist subgraph_partition tanner