induction ls; intuition; simpl in *.
econstructor.
destruct (in_dec (EqDec_dec eqd) a ls).
discriminate.
econstructor; intuition.
inversion H1; clear H1; subst.
destruct (in_dec (EqDec_dec eqd) a ls);
intuition.
Qed.

Theorem hasDups_true_not_NoDup :
forall (A : Set)(eqd : EqDec A)(ls : list A),
hasDups eqd ls = true <-> (~ NoDup ls).