proposition: Lemma formB u v : let d := '[u, v] in '[u - v] = '[u] + '[v] - (d + (-1) ^+ eps * theta d).
proof: Proof. by rewrite formD formN !formNr rmorphN mulrN -opprD. Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix mxalgebra vector falgebra ssrnum algC algnum) mathcomp(fieldext) mathcomp(vector)