Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  x : A
  y : B
  l : list A
  l' : list B
  r : R x y
  rs : All2 R l l'
  r0 : R' x y r
  a0 : All2_dep R' rs
  r2 : R' x y r
  b : All2_dep R' rs
  ============================
   (NoConfusionHom_All2_dep A B R R' (x :: l) (y :: l') 
      (All2_cons r rs) (All2_dep_cons r0 a0) (All2_dep_cons r2 b)
    → let H := CoreTactics.block in All2_dep_cons r0 a0 = All2_dep_cons r2 b)


DEBUG:Going to execute:
try (intro; CoreTactics.intros_until_block)