Goal:
  
  A : Type
  B : Type
  P : B → A → A → Type
  b : B
  bs : list B
  hd : A
  tl : list A
  tl' : list A
  h : OnOne2All P bs tl tl'
  i' : B
  x : A
  y : A
  u : list A
  v : list A
  a : P i' x y
  H : tl = u ++ x :: v
  H0 : tl' = u ++ y :: v
  ============================
   (hd :: tl = (hd :: u) ++ x :: v)


DEBUG:Going to execute:
F x2 x1 x0
Level 0: Backtrace:

P is used in hypothesis h.
Level 0: Backtrace:

P is used in hypothesis h.
Level 0: Backtrace:

P is used in hypothesis h.
Level 0: Backtrace:

P is used in hypothesis h.
Level 0: Backtrace:

P is used in hypothesis h.
Level 1: Backtrace:

P is used in hypothesis h.
Level 0: Backtrace:

P is used in hypothesis h.