Goal:
    G1 : t  G2 : t  s : VSet.t  x : V.t  y : V.t  p : SPath G2 s x y
  ============================
   (forall (s2 : VSet.t) (x0 z0 : V.t) (s1 : VSet.t) (y0 : V.t),
    DisjointAdd x0 s1 s2 ->
    EdgeOf G2 x0 y0 ->
    forall q : SPath G2 s1 y0 z0,
    (VSet.In y0 (V G1) -> first_in q = y0) ->
    VSet.mem x0 (V G1) = false -> VSet.In x0 (V G1) -> first_in q = x0)


DEBUG:Going to execute:
<coq-core.plugins.ssreflect::ssrmove@1> $1 $2
Level 0: Backtrace:

No matching clauses for match.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.
Level 1: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.