fact: Variable smith2x2 : 'M[R]_2 -> 'M[R]_2 * seq R * 'M[R]_2.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype matrix mxalgebra bigop zmodp perm choice) dvdring mxstructure minor stronglydiscrete coherent edr