In Hickman v. Taylor, 329 U.S. 495 (1947), the question was whether written and oral statements of witnesses obtained by defense counsel in a potential wrongful death case as well as notes and memorandums prepared by the attorney concerning the possible litigation should be produced for examination by opposing counsel. The Supreme Court held that the witnesses' statements and defense counsel's memorandums were not within the attorney-client privilege ( id., at p. 508); however, the notes prepared by the attorney were the "work-product" of the attorney and should not be produced absent a showing of absolute necessity at trial ( id., at pp. 510-514). Hickman speaks to discovery of information acquired by opposing counsel "in the course of preparation for possible litigation after a claim has arisen." ( Id., at p. 497.) Justice Jackson concurred by saying "discovery was hardly intended to enable a learned profession to perform its functions either without wits or on wits borrowed from the adversary." ( Id., at p. 516.) The Supreme Court stated that it is essential that a lawyer work with a degree of privacy, "free from intrusion by opposing parties and their counsel," and that if such materials as the attorney's notes, mental impressions, briefs, etc., "were open to opposing counsel on mere demand, much of what is now put down in writing would remain unwritten." (Id. at 510-511.) The Supreme Court stated that a demand for such material, without a showing of necessity, "falls outside the arena of discovery and contravenes the public policy underlying the orderly prosecution and defense of legal claims." (Id. at 510.) In short, work product immunity protects the adversarial process by fostering the attorney's adequate preparation. Work product is immune from disclosure under CPLR 3101 (c). The United States Supreme Court held that oral and written statements of witnesses obtained or prepared by an adverse party's counsel in the course of preparation for possible litigation are not discoverable without a showing of necessity. In effect, the Hickman Court recognized the attorney-work product rule, which is "a qualified privilege for witness statements prepared at the request of the attorney and an almost absolute privilege for attorney notes taken during a witness interview." In re PCB, 167 Vt. 379, 708 A.2d 568 (Vt. 1998); see also Hickman, 329 U.S. at 495. Also, under the attorney-work product rule, the mental impressions, conclusions, opinions and legal theories of an attorney are absolutely protected from discovery regardless of any showing of need. See Hickman, 329 U.S. at 495. Indeed, North Carolina recognizes the attorney-work product rule under N.C. Gen. Stat. 1A-1, Rule 26(b)(3) (1990). Under that statute, attorney-work product is defined in relevant part to include, among other things, materials "prepared in anticipation of litigation or for trial by or for another party or by or for that other party's . . . agent . . . ." Id. Such evidence may be obtained by a party "only upon a showing that the party seeking discovery has substantial need of the materials in the preparation of his case and that he is unable without undue hardship to obtain the substantial equivalent of the materials by other means." Id. Our courts have previously considered the attorney-client privilege, and held that it may be waived by the client when he or she offers testimony concerning the substance of the privileged communication. See: State v. Tate, 294 N.C. 189, 239 S.E.2d 821 (1978) (holding that the defendant by eliciting testimony regarding a letter written to him by his attorney, waived the attorney-client privilege with respect to the entire content of the letter); Hayes v. Ricard, 244 N.C. 313, 93 S.E.2d 540 (1956) (holding that when plaintiffs elected to examine the decedent's former attorney, plaintiffs waived their right to keep privileged the communications between that attorney and the decedent); State v. Artis, 227 N.C. 371, 42 S.E.2d 409 (1947) (holding that the State could cross-examine as to an alleged privileged communication between the defendant and his attorney where the defendant first brought out testimony on the subject). Twenty-eight years following the Hickman decision, in United States v. Nobles, 422 U.S. 225, 45 L. Ed. 2d 141, 95 S. Ct. 2160 (1975), the United States Supreme Court extended the work-product doctrine from the pre-trial context to trial, reasoning that "the concerns reflected in the work-product doctrine do not disappear once trial has begun." Nobles, 422 U.S. at 239, 45 L. Ed. 2d at 154. The Supreme Court recognized that the protection afforded by "the work product doctrine is not absolute. Like other qualified privileges, it may be waived." Id. The Supreme Court held that the qualified privilege derived from the attorney-work product rule was waived with respect to those matters covered in an investigator's testimony and as a result, the rule was not available to prevent disclosure of the relevant portions of the investigator's report. In reaching this holding, the Supreme Court stated that "respondent, by electing to present the investigator as a witness, waived the privilege with respect to matters covered in his testimony." Id. The Court further noted by analogy that: Respondent can no more advance the work-product doctrine to sustain a unilateral testimonial use of work-product materials than he could elect to testify in his own behalf and thereafter assert his Fifth Amendment privilege to resist cross-examination on matters reasonably related to those brought out in direct examination. Nobles, 422 U.S. at 239-40, 45 L. Ed. 2d at 154.