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:
match goal with
           | |- ?T => change (let _ := CoreTactics.block in T)
           end