Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  l : list A
  r2 : list B
  h : All2 R l ([] ++ r2)
  ============================
   (l = [] ++ l × All2 R [] [] × All2 R l r2)


DEBUG:Going to execute:
<coq-core.plugins.ltac::eauto@0> $1 $2 $3