intelligent plea

a defendant's plea of guilty based on reasonably competent advice is an intelligent plea not open to attack on the ground that counsel may have misjudged the admissibility of the defendant's confession; whether a plea of guilty is unintelligent and therefore vulnerable when motivated by a confession erroneously thought admissible in evidence depends as an initial matter, not on whether a court would retrospectively consider counsel's advice to be right or wrong, but on whether that advice was within the range of competence demanded of attorneys in criminal cases