proposition: Lemma lagrange_sample (i j : 'I_n) : (lagrange_ i).[x j] = (i == j)%:R.
proof: Proof. by rewrite lagrangeE lagrange_def_sample. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice fintype tuple) mathcomp(bigop binomial finset finfun ssralg countalg finalg poly polydiv) mathcomp(perm fingroup matrix mxalgebra mxpoly vector countalg)