(** We also provide two tactics [pdestruct] and [pinversion]. They are simply defined as follows:  - [pdestruct H] := [punfold H; destruct H; pclearbot] - [pinversion H] := [punfold H; inversion H; pclearbot]  Using this the proof of the above theorem [seq'_cons] can be simplified as [intros; pinversion SEQ; auto.] *)(* *)
(** ** Example: infinite tree equality  The second example involves infinite binary trees of natural numbers and an equality thereon.  We prove two particular equalities via [cofix] in an incremental fashion, and then show how these proofs can be done just as easily via [pcofix]. We then show how, using [pcofix], the proofs can additionally be modularly decomposed.  *)
(** As before, we first define the coinductive type and the unfolding trick. *)
CoInductive inftree :=
| node : nat -> inftree -> inftree -> inftree.
Definition tunf t : inftree :=
match t with node n tl tr => node n tl tr end.

Lemma tunf_eq : forall t, t = tunf t.
CoFixpoint one : inftree := node 1 one two
with       two : inftree := node 2 one two.