• 3 It is the function of the trier of fact to weigh the testimony, judge the credibility of the witnesses and determine factual matters in debatable sets of circumstances ( People v. Akis, 63 Ill.2d 296, 347 N.E.2d 733; People v. Morse, 33 Ill. App.3d 384, 342 N.E.2d 307), and, in a criminal proceeding, the trier of fact may believe part of one's testimony without believing all of it. ( People v. Holverson, 32 Ill. App.3d 459, 336 N.E.2d 88. See also In re Morgan, 35 Ill. App.3d 10, 341 N.E.2d 19.) A reviewing court has neither the duty nor privilege to substitute its judgment as to the weight of disputed evidence or credibility of witnesses for that of the trier of fact.