Goal:
    A : Type  B : Type  C : Type  R : A → B → C → Type  b0 : All3 R [] [] []
  ============================
   ({|
      pr1 := {| pr1 := []; pr2 := {| pr1 := []; pr2 := [] |} |}; pr2 := b0
    |} =
    {|
      pr1 := {| pr1 := []; pr2 := {| pr1 := []; pr2 := [] |} |};
      pr2 := All3_nil
    |}
    → let H := CoreTactics.block in
      NoConfusionHom_All3 A B C R [] [] [] All3_nil b0
      → let H0 := CoreTactics.block in All3_nil = b0)


DEBUG:Going to execute:
simplify * || simplify ?; cbv beta