Goal:
  
  A : Type
  a : A
  l : list A
  a0 : A
  l' : list A
  r : list A
  r' : list A
  IHl : ∀ l' r r' : list A,
          l ++ r = l' ++ r' → #|l| = #|l'| → l = l' ∧ r = r'
  H : a :: l ++ r = a0 :: l' ++ r'
  H0 : S #|l| = S #|l'|
  ============================
   (a :: l = a0 :: l' ∧ r = r')


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

No primitive equality found.
Level 0: Backtrace:

No primitive equality found.