fact: Definition vsolve_eq U := finfun (tnth rhs) \in (linfun lhsf @: U)%VS.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)