fact: Definition dest_port := [set x : port * {set port} | [&& x.1 \in free_coports, x.1 \in x.2 & trivIset (x.2 |: conodes c)]].
imports: mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix perm) ssr_ext ssralg_ext fdist subgraph_partition tanner