intuition.
rewrite (@Permutation_length _ _ (forNats n)).
eapply forNats_length.
eapply NoDup_Permutation.
eapply getSupport_NoDup.
eapply forNats_NoDup.
intuition.
eapply forNats_In.
eapply RndNat_support_lt; intuition.
eapply in_getSupport_RndNat.
eapply forNats_In; intuition.
Qed.

Theorem RndNat_prob :
forall n i (nzn : nz n),
i < n ->
evalDist (RndNat n) i == 1 / n.