Goal:
    A : Type  B : Type  P : A → B → Type  Q : A → B → Type  H : All2 Q [] []
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in All2 (Trel_conj P Q) [] [])


DEBUG:Going to execute:
DepElim.generalize_sig_gen id
            ltac:(fun id id' id'1 t =>
                    try rename id into id',id' into id; cont id'1 id)