McCutcheon pled guilty to that count. As this Court held in Ochoa v. United States, 5 Cir. 1972, 469 F.2d 86, a plea of guilty does not raise the problem of the unconstitutional presumption because a guilty plea is obtained without the aid of the impermissible presumption. Accord, Yohey v. United States, 5 Cir. 1970, 429 F.2d 1279.