Goal:
  
  A : Type
  P : list A → A → Type
  b : All_fold P []
  b0 := {| pr1 := []; pr2 := b |}
     : sigma (λ index : list A, All_fold P index)
  ============================
   ({| pr1 := []; pr2 := b |} = b0
    → let H := CoreTactics.block in
      NoConfusionHom_All_fold A P [] (All_fold_nil P) b
      → let H0 := CoreTactics.block in All_fold_nil P = b)


DEBUG:Going to execute:
clearbody id'
DEBUG LTAC Evaluated term: (eq_refl : {| pr1 := []; pr2 := b |} = b0)