Goal:
    A : Type  B : Type  R : nat → A → B → Type  n : nat
  ============================
   (NoConfusionHom_All2i A B R n [] [] All2i_nil All2i_nil
    → let H := CoreTactics.block in All2i_nil = All2i_nil)


DEBUG:Going to execute:
<coq-core.plugins.ltac::intro@0>