Goal:
  
  A : Type
  B : Type
  P : A → B → Type
  Q : A → B → Type
  x : A
  y : B
  l : list A
  l' : list B
  r : P x y
  X : All2 P l l'
  IHX : All2 Q l l' → All2 (Trel_conj P Q) l l'
  H1' : list A
  H1 : list B
  H : All2 Q H1' H1
  ============================
   ({| pr1 := x :: l; pr2 := y :: l' |} = {| pr1 := H1'; pr2 := H1 |}
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in All2 (Trel_conj P Q) (x :: l) (y :: l'))


DEBUG:Going to execute:
let ty := type of p in
           let eliminator := eval simpl in DepElim.elim in
           tac p eliminator