intuition.
eapply getSupport_In_evalDist.
intuition.
rewrite H in H1.
clear H.
unfold marginal_r in *.
simpl in *.
eapply sumList_0 in H1; eauto.
eapply ratMult_0 in H1.
intuition.
eapply getSupport_In_evalDist;
eauto.
dist_compute.
Qed.
Definition comp_spec (R1 R2 : Set)
{eqd1 : EqDec R1}{eqd2 : EqDec R2}
(post : R1 -> R2 -> Prop)(c1 : Comp R1)(c2 : Comp R2) :=
exists c : Comp (R1 * R2),
(forall r1, evalDist c1 r1 == marginal_l c r1) /\
(forall r2, evalDist c2 r2 == marginal_r c r2) /\
(forall p, In p (getSupport c) -> post (fst p) (snd p)).

Theorem list_choice :
forall (A B : Type)(eqd : forall (a1 a2 : A), {a1 = a2} + {a1 <> a2}) P (ls : list A) (b : B),
(forall a, In a ls -> exists (b : B), P a b) ->
exists (f : A -> B), (forall a, In a ls -> P a (f a)).