Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  d : A
  Γ0 : list A
  a : A
  Γ' : list A
  Hrel : All2_fold P Γ0 Γ'
  p : P Γ0 Γ' d a
  ============================
   (∑ d0 : A, Some d = Some d0 × All2_fold P Γ0 Γ' × P Γ0 Γ' d0 a)


DEBUG:Going to execute:
eexists