Notation "\big [ op / idx ]_ ( i < n ) F" :=
  (\big[op/idx]_(i : ordinal n) F) : big_scope.Local Notation "x + y" := (plus x y).Notation "\max_ ( i 'in' A ) F" :=
 (\big[maxn/0%N]_(i in A) F%N) : nat_scope.

Lemma big_rec I r (P : pred I) F (Kop : forall i x, P i -> K x -> K (op (F i) x)) : K (\big[op/idx]_(i <- r | P i) F i).