fact: Definition PCM_instance (y : 'rV[letter]_n) := \matrix_(i < m, j < n) if i \in 'F j then y ``_ j else Blank.
imports: mathcomp(all_ssreflect ssralg fingroup finalg perm zmodp) mathcomp(matrix) f2 ssr_ext ssralg_ext max_subset num_occ hamming ldpc_erasure tanner linearcode