Goal:
  
  A : Type
  B : Type
  P : A → B → Type
  l1 : list A
  l2 : list A
  r1 : list B
  r2 : list B
  e : #|l1| = #|r1|
  w1 : list B
  w2 : list B
  e1 : r1 ++ r2 = w1 ++ w2
  h1 : #|l1| = #|w1|
  h2 : #|l2| = #|w2|
  ============================
   (#|r1| = #|w1|)


DEBUG:Going to execute:
<coq-core.plugins.cc::cc@0> $1
DEBUG LTAC Evaluated term: All2_length
DEBUG LTAC Evaluated term: All2_length