Section RightInduction.
Let A' (n : t) := forall m, z <= m -> m < n -> A m.
Let right_step :=   forall n, z <= n -> A n -> A (S n).
Let right_step' :=  forall n, z <= n -> A' n -> A n.
Let right_step'' := forall n, A' n <-> A' (S n).

Lemma rbase : A' z.