fact: Definition diag_seqmx (s : seqmx) := mkseqmx_ord (fun (i j : 'I_(size (nth [::] s 0))) => (if i == j then nth 0%C (nth [::] s 0) i else 0%C)).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq ssralg) mathcomp(path choice fintype tuple finset bigop poly matrix mxpoly) CoqEAL(hrel param refinements trivial_seq)