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:
match goal with
           | hyp:context [ CoreTactics.block ]
             |- _ =>
                 cbn beta in hyp; eqns_specialize_eqs_block hyp;
                  cbn[eq_rect_r eq_rect] in hyp
           end