induction arr; intuition; simpl in *.
case_eq (eqb a a0); intuition.
rewrite eqb_leibniz in H0.
subst.
intuition.
Qed.
Fixpoint arrayLookupOpt(A B : Set)(eqd : EqDec A)(ls : list (option (A * B)))(a : A) :=
match ls with
| nil => None
| o :: ls' =>
match o with
| None => arrayLookupOpt _ ls' a
| Some (a', b') =>
if (eqb a a') then (Some b') else (arrayLookupOpt _ ls' a)
end
end.

Theorem list_pred_arrayLookupOpt :
forall (A B C : Set)(P : B -> C -> Prop)(eqda : EqDec A)(ls1 : list (option (A * B)))(ls2 : list (option (A * C))),
list_pred (fun o1 o2 =>
match o1 with
| None => o2 = None
| Some x =>
match o2 with
| None => False
| Some y =>
fst x = fst y /\ P (snd x) (snd y)
end
end) ls1 ls2 ->
forall a,
match (arrayLookupOpt _ ls1 a) with
| None => (arrayLookupOpt _ ls2 a) = None
| Some x => exists y, (arrayLookupOpt _ ls2 a) = Some y /\ P x y
end.