Goal:
    A : Type  P : list A → list A → A → A → Type
  ============================
   (let H := CoreTactics.block in
    NoConfusion_All2_fold A P
      {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |}
      {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |}
    → let H0 := CoreTactics.block in
      {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |} =
      {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |})


DEBUG:Going to execute:
change T; CoreTactics.intros_until_block
Level 5: T
 has value 
(NoConfusion_All2_fold A P
   {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |}
   {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |}
 → let H := CoreTactics.block in
   {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |} =
   {| pr1 := {| pr1 := []; pr2 := [] |}; pr2 := All2_fold_nil P |})