Goal:
  
  A : Type
  P : list A → A → Type
  b : All_fold P []
  H : NoConfusionHom_All_fold A P [] (All_fold_nil P) b
  ============================
   (All_fold_nil P = b)


DEBUG:Going to execute:
DepElim.is_introduced H; CoreTactics.block_goal;
            CoreTactics.revert_until H; CoreTactics.block_goal