fact: Definition mxSum M := \matrix_(i < m, j < n) if i \in 'F j then Sum (rowVnextD1 (row i M) i j) else M i j.
imports: mathcomp(all_ssreflect ssralg fingroup finalg perm zmodp) mathcomp(matrix) ssr_ext ssralg_ext num_occ f2 ssrR hamming tanner linearcode