proposition: Lemma formD u v : let d := '[u, v] in '[u + v] = '[u] + '[v] + (d + (-1) ^+ eps * theta d).
proof: Proof. by rewrite formDl !formDr ['[v, _]]formC [_ + '[v]]addrC addrACA. Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix mxalgebra vector falgebra ssrnum algC algnum) mathcomp(fieldext) mathcomp(vector)