Goal:
    A : Type  P : list A → A → Type  H : True
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in All_fold_nil P = All_fold_nil P)


DEBUG:Going to execute:
fun p =>
             DepElim.introduce p;
              DepElim.elim_case p || destruct p || (case p; clear p)