Goal:
  
  A : Type
  P : list A → A → Type
  d : A
  Γ : list A
  a : All_fold P Γ
  p : P Γ d
  b : All_fold P Γ
  p0 : P Γ d
  H0 := {| pr1 := b; pr2 := p0 |} : sigma (λ _ : All_fold P Γ, P Γ d)
  H : {| pr1 := a; pr2 := p |} = H0
  ============================
   (All_fold_cons P a p = All_fold_cons P b p0)


DEBUG:Going to execute:
pattern sigma rhs
DEBUG LTAC Evaluated term: {| pr1 := b; pr2 := p0 |}