Goal:
  
  A : Type
  B : Type
  P : B → A → A → Type
  i : list B
  i' : list B
  l : list A
  tl : list A
  tl' : list A
  ============================
   (OnOne2All P i tl tl'
    → #|i'| = #|l| → OnOne2All P (i' ++ i) (l ++ tl) (l ++ tl'))


DEBUG:Going to execute:
induction l in i, i' |- *; simpl; try constructor