Goal:
  
  A : Type
  P : list A → A → Type
  b : All_fold P []
  b0 : 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:
try rename id into id',id' into id
Level 4: evaluation returns
try rename id into id',id' into id; cont id'1 id
where
t := {| pr1 := []; pr2 := b |}
of type
constr
id'1 := b
of type
constr
id' := b0
of type
constr
id := b
of type
constr
cont := fun id id' => DepElim.decompose_exists id id'
        where
        id := b
        of type
        constr
of type
tacvalue of type tacvalue