--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+include "ground/relocation/tr_compose_pap.ma".
+include "ground/relocation/tr_uni_pap.ma".
+include "delayed_updating/syntax/path.ma".
+include "delayed_updating/notation/functions/black_downtriangle_4.ma".
+include "delayed_updating/notation/functions/black_downtriangle_2.ma".
+
+(* UNWIND FOR PATH **********************************************************)
+
+definition unwind_continuation (A:Type[0]) ≝
+tr_map → path → A.
+
+rec definition unwind_gen (A:Type[0]) (k:unwind_continuation A) (f) (p) on p ≝
+match p with
+[ list_empty ⇒ k f (𝐞)
+| list_lcons l q ⇒
+ match l with
+ [ label_d n ⇒
+ match q with
+ [ list_empty ⇒ unwind_gen (A) (λg,p. k g (𝗱(f@❨n❩)◗p)) (f∘𝐮❨n❩) q
+ | list_lcons _ _ ⇒ unwind_gen (A) k (f∘𝐮❨n❩) q
+ ]
+ | label_m ⇒ unwind_gen (A) k f q
+ | label_L ⇒ unwind_gen (A) (λg,p. k g (𝗟◗p)) (⫯f) q
+ | label_A ⇒ unwind_gen (A) (λg,p. k g (𝗔◗p)) f q
+ | label_S ⇒ unwind_gen (A) (λg,p. k g (𝗦◗p)) f q
+ ]
+].
+
+interpretation
+ "unwind (gneric)"
+ 'BlackDownTriangle A k f p = (unwind_gen A k f p).
+
+definition proj_path: unwind_continuation … ≝
+ λf,p.p.
+
+definition proj_rmap: unwind_continuation … ≝
+ λf,p.f.
+
+interpretation
+ "unwind (path)"
+ 'BlackDownTriangle f p = (unwind_gen ? proj_path f p).
+
+interpretation
+ "unwind (relocation map)"
+ 'BlackDownTriangle p f = (unwind_gen ? proj_rmap f p).
+
+(* Basic constructions ******************************************************)
+
+lemma unwind_empty (A) (k) (f):
+ k f (𝐞) = ▼{A}❨k, f, 𝐞❩.
+// qed.
+
+lemma unwind_d_empty_sn (A) (k) (n) (f):
+ ▼❨(λg,p. k g (𝗱(f@❨n❩)◗p)), f∘𝐮❨ninj n❩, 𝐞❩ = ▼{A}❨k, f,
+𝗱n◗𝐞❩.
+// qed.
+
+lemma unwind_d_lcons_sn (A) (k) (p) (l) (n) (f):
+ ▼❨k, f∘𝐮❨ninj n❩, l◗p❩ = ▼{A}❨k, f, 𝗱n◗l◗p❩.
+// qed.
+
+lemma unwind_m_sn (A) (k) (p) (f):
+ ▼❨k, f, p❩ = ▼{A}❨k, f, 𝗺◗p❩.
+// qed.
+
+lemma unwind_L_sn (A) (k) (p) (f):
+ ▼❨(λg,p. k g (𝗟◗p)), ⫯f, p❩ = ▼{A}❨k, f, 𝗟◗p❩.
+// qed.
+
+lemma unwind_A_sn (A) (k) (p) (f):
+ ▼❨(λg,p. k g (𝗔◗p)), f, p❩ = ▼{A}❨k, f, 𝗔◗p❩.
+// qed.
+
+lemma unwind_S_sn (A) (k) (p) (f):
+ ▼❨(λg,p. k g (𝗦◗p)), f, p❩ = ▼{A}❨k, f, 𝗦◗p❩.
+// qed.
+
+(* Basic constructions with proj_path ***************************************)
+
+lemma unwind_path_empty (f):
+ (𝐞) = ▼[f]𝐞.
+// qed.
+
+lemma unwind_path_d_empty_sn (f) (n):
+ 𝗱(f@❨n❩)◗𝐞 = ▼[f](𝗱n◗𝐞).
+// qed.
+
+lemma unwind_path_d_lcons_sn (f) (p) (l) (n):
+ ▼[f∘𝐮❨ninj n❩](l◗p) = ▼[f](𝗱n◗l◗p).
+// qed.
+
+lemma unwind_path_m_sn (f) (p):
+ ▼[f]p = ▼[f](𝗺◗p).
+// qed.
+
+(* Basic constructions with proj_rmap ***************************************)
+
+lemma unwind_rmap_empty (f):
+ f = ▼[𝐞]f.
+// qed.
+
+lemma unwind_rmap_d_sn (f) (p) (n):
+ ▼[p](f∘𝐮❨ninj n❩) = ▼[𝗱n◗p]f.
+#f * // qed.
+
+lemma unwind_rmap_m_sn (f) (p):
+ ▼[p]f = ▼[𝗺◗p]f.
+// qed.
+
+lemma unwind_rmap_L_sn (f) (p):
+ ▼[p](⫯f) = ▼[𝗟◗p]f.
+// qed.
+
+lemma unwind_rmap_A_sn (f) (p):
+ ▼[p]f = ▼[𝗔◗p]f.
+// qed.
+
+lemma unwind_rmap_S_sn (f) (p):
+ ▼[p]f = ▼[𝗦◗p]f.
+// qed.
+
+(* Advanced constructions with proj_rmap and path_append ********************)
+
+lemma unwind_rmap_append (p2) (p1) (f):
+ ▼[p2]▼[p1]f = ▼[p1●p2]f.
+#p2 #p1 elim p1 -p1 // * [ #n ] #p1 #IH #f //
+[ <unwind_rmap_m_sn <unwind_rmap_m_sn //
+| <unwind_rmap_A_sn <unwind_rmap_A_sn //
+| <unwind_rmap_S_sn <unwind_rmap_S_sn //
+]
+qed.
+
+(* Advanced constructions with proj_rmap and path_rcons *********************)
+
+lemma unwind_rmap_d_dx (f) (p) (n):
+ (▼[p]f)∘𝐮❨ninj n❩ = ▼[p◖𝗱n]f.
+// qed.
+
+lemma unwind_rmap_m_dx (f) (p):
+ ▼[p]f = ▼[p◖𝗺]f.
+// qed.
+
+lemma unwind_rmap_L_dx (f) (p):
+ (⫯▼[p]f) = ▼[p◖𝗟]f.
+// qed.
+
+lemma unwind_rmap_A_dx (f) (p):
+ ▼[p]f = ▼[p◖𝗔]f.
+// qed.
+
+lemma unwind_rmap_S_dx (f) (p):
+▼[p]f = ▼[p◖𝗦]f.
+// qed.
+
+lemma unwind_rmap_pap_d_dx (f) (p) (n) (m):
+ ▼[p]f@❨m+n❩ = ▼[p◖𝗱n]f@❨m❩.
+#f #p #n #m
+<unwind_rmap_d_dx <tr_compose_pap <tr_uni_pap //
+qed.
+
+(* Advanced eliminations with path ******************************************)
+
+lemma path_ind_unwind (Q:predicate …):
+ Q (𝐞) →
+ (∀n. Q (𝐞) → Q (𝗱n◗𝐞)) →
+ (∀n,l,p. Q (l◗p) → Q (𝗱n◗l◗p)) →
+ (∀p. Q p → Q (𝗺◗p)) →
+ (∀p. Q p → Q (𝗟◗p)) →
+ (∀p. Q p → Q (𝗔◗p)) →
+ (∀p. Q p → Q (𝗦◗p)) →
+ ∀p. Q p.
+#Q #IH1 #IH2 #IH3 #IH4 #IH5 #IH6 #IH7 #p
+elim p -p [| * [ #n * ] ]
+/2 width=1 by/
+qed-.