Section Abelian.
Variable op : Monoid.com_law 1.
Local Notation "'*%M'" := op (at level 0).
Local Notation "x * y" := (op x y).
Arguments bigID [I r].
Arguments bigD1 [I] j [P F].

Lemma bigD1_seq (I : eqType) (r : seq I) j F :
j \in r -> uniq r ->
\big[*%M/1]_(i <- r) F i = F j * \big[*%M/1]_(i <- r | i != j) F i.