Goal:
  
  A : Type
  B : Type
  C : Type
  R : A → B → C → Type
  b : All3 R [] [] []
  e : NoConfusionHom_All3 A B C R [] [] [] All3_nil b
  ============================
   (let H := CoreTactics.block in
    noConfusionHom_All3_obligation_2 A B C R [] [] [] All3_nil b
      (noConfusionHom_All3_obligation_1 A B C R [] [] [] All3_nil b e) = e)


DEBUG:Going to execute:
tac H