Goal:
  
  G1 : t
  G2 : t
  H : invariants G1
  ext := EdgeSet.diff (E G2) (E G1) : EdgeSet.t
  bs := border_set G1 ext : VSet.t
  s : VSet.t
  y : V.t
  z : V.t
  p : SPath G2 s y z
  _s2_ : VSet.t
  _x0_ : V.t
  _z0_ : V.t
  _s1_ : VSet.t
  _y0_ : V.t
  _d_ : DisjointAdd _x0_ _s1_ _s2_
  _e_ : EdgeOf G2 _x0_ _y0_
  _q_ : SPath G2 _s1_ _y0_ _z0_
  __view_subject_1_ : VSet.In _x0_ (V G1)
  _x_ : V.t
  _projT1_ : Z
  _hz_ : VSet.In _z0_ (V G1)
  e := (_x_, _projT1_, _x0_) : (V.t × Z) × V.t
  _he_ : EdgeSet.In e ext
  ============================
   (_x0_ = e..s)


DEBUG:Going to execute:
repeat
            (match reverse goal with
             | id:?X1
               |- _ =>
                   <Coq.Init.Tauto.is_conj> flags X1; elim id; do 2 intro;
                    clear id
             | id:_ <-> _ |- _ => elim id; do 2 intro; clear id
             | id:~ _ |- _ => red in id
             | id:?X1
               |- _ =>
                   <Coq.Init.Tauto.is_disj> flags X1; elim id; intro; clear
                    id
             | _ =>
                 <Coq.Init.Tauto.find_cut>
                  ltac:(fun id0 id1 X2 =>
                          assert X2; [ exact (id0 id1) | clear id0 ])
             | id:?X1 -> ?X2
               |- _ =>
                   <Coq.Init.Tauto.is_unit_or_eq> flags X1; Ltac.cut X2;
                    [ intro; clear id
                    | Ltac.cut X1; [ exact id | constructor 1; fail ] ]
             | id:?X1 -> ?X2
               |- _ =>
                   <Coq.Init.Tauto.flatten_contravariant_conj> flags X1 X2 id
             | id:?X1 <-> ?X2 -> ?X3
               |- _ =>
                   assert ((X1 -> X2) -> (X2 -> X1) -> X3) by
                    (do 2 intro; apply id; Ltac.split; Ltac.assumption);
                    clear id
             | id:?X1 -> ?X2
               |- _ =>
                   <Coq.Init.Tauto.flatten_contravariant_disj> flags X1 X2 id
             | |- ?X1 => <Coq.Init.Tauto.is_conj> flags X1; Ltac.split
             | |- _ <-> _ => Ltac.split
             | |- ~ _ => red
             end; <Coq.Init.Tauto.not_dep_intros>)
Level 1: Backtrace:

No matching clauses for match.