Arguments bigID [I r].

(* Specifications: *)
Lemma bigU (I : finType) (A B : pred I) F :
[disjoint A & B] ->
\big[*%M/1]_(i in [predU A & B]) F i =
(\big[*%M/1]_(i in A) F i) * (\big[*%M/1]_(i in B) F i).
Lemma bigD1 (I : finType) j (P : pred I) F :
P j -> \big[*%M/1]_(i | P i) F i
= F j * \big[*%M/1]_(i | P i && (i != j)) F i.