. . . "present[s] to the court (whether by signing, filing, submitting, or later advocating) a pleading, written motion, or other paper, ... is certifying that to the best of the person's knowledge, information, and belief, formed after an inquiry reasonable under the circumstances, ... (2) the claims, defenses, and other legal contentions therein are warranted by existing law or by a nonfrivolous argume" .