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


DEBUG:Going to execute:
CoreTactics.intros_until_block