In Jennings v. Superior Court (1967) 66 Cal.2d 867, the California Supreme Court rejected the argument that because the purpose of the preliminary hearing is limited to a determination of probable cause, defendant's rights to cross-examination and to present an affirmative defense are curtailed. At page 880, the court stated, " 'The preliminary examination is not merely a pretrial hearing. "The purpose of the preliminary hearing is to weed out groundless or unsupported charges of grave offenses, and to relieve the accused of the degradation and expense of a criminal trial. Many an unjustifiable prosecution is stopped at that point, where the lack of probable cause is clearly disclosed." '... To effectuate this constitutional and statutory purpose the defendant must be permitted, if he chooses, to elicit testimony or introduce evidence tending to overcome the prosecution's case or establish an affirmative defense."