--- /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 *)
+(* *)
+(**************************************************************************)
+
+
+
+(* PROOF TREE TRACKS
+*)
+
+include "Insert/defs.ma".
+
+inductive Track: Context \to Proof \to Sequent \to Prop \def
+ | track_proj: \forall P,Q,p1,p2,S,i.
+ Insert p1 p2 S i P Q \to Track Q (lref i) S
+ | track_posr: \forall P,h.
+ Track P (prin h) (pair (posr h) (posr h))
+ | track_impw: \forall P,r,D,a,b. Track P r (pair lleaf D) \to
+ Track P (impw r) (pair (impl a b) D)
+ | track_impr: \forall P,r. \forall a,b:Formula.
+ Track P r (pair a b) \to
+ Track P (impr r) (pair lleaf (impl a b))
+ | track_impi: \forall P,p,q,r,A,B,D. \forall a,b:Formula.
+ Track P p (pair A a) \to
+ Track P q (pair b B) \to
+ Track (abst P p q (pair A B)) r (pair lleaf D) \to
+ Track P (impi p q r) (pair (impl a b) D)
+ | track_scut: \forall P,p,q,A,B. \forall c:Formula.
+ Track P p (pair A c) \to
+ Track P q (pair c B) \to
+ Track P (scut p q) (pair A B)
+.