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
  H : {| pr1 := a; pr2 := p |} = {| pr1 := b; pr2 := p0 |}
  ============================
   (All_fold_cons P a p = All_fold_cons P b p0)


DEBUG:Going to execute:
let rhs := fresh in
           set (rhs := y) in *; pattern sigma rhs; clearbody rhs; destruct H;
            simpl
DEBUG LTAC Evaluated term: H
DEBUG LTAC Evaluated term: ({| pr1 := a; pr2 := p |} =
                            {| pr1 := b; pr2 := p0 |})
Level 6: type of H
 has value 
({| pr1 := a; pr2 := p |} = {| pr1 := b; pr2 := p0 |})