Although the defendant's failure to specifically raise a contention normally constitutes a waiver ( People v. Precup (1978), 73 Ill.2d 7, 16, 382 N.E.2d 227), the waiver rule is a limitation on the parties and not on the courts, and a reviewing court may ignore the waiver in the interest of substantial justice. People v. Walsh (1981), 101 Ill. App.3d 1146, 1149, 428 N.E.2d 937. We observe that the defendant was sentenced to extended terms for both murder and robbery, the former being a separate and higher classification of offense from robbery which is a Class 2 felony.

Thus, when a reviewing court issues a mandate, it vests the trial court with jurisdiction to take only such action as conforms to that mandate. (See PSL Realty Co. v. Granite Investment Co. (1981), 86 Ill.2d 291, 309; Thomas v. Durchslag (1951), 410 Ill. 363, 366; People v. Walsh (1981), 101 Ill. App.3d 1146, 1147-48; People v. Lowther (1980), 85 Ill. App.3d 735, 739; People v. Baker (1980), 85 Ill. App.3d 661, 662.) Any other order issued by the trial court is outside the scope of its authority and void for lack of jurisdiction.

Nevertheless, here, as elsewhere, the waiver rule is a limitation on the parties and not on the courts. People v. Walsh, 101 Ill. App.3d 1146, 1149, 428 N.E.2d 937, 940 (1981). In this case, we choose to proceed to the merits of the new issue.

We need not decide whether the reasoning in Williams applies to this case because while waiver is an admonition to the parties, it is not a limitation upon the reviewing court. People v. Lann, 261 Ill. App.3d 456, 470, 633 N.E.2d 938, 949 (1994); People v. Walsh, 101 Ill. App.3d 1146, 1149, 428 N.E.2d 937, 940 (1981). It is a rule of administrative convenience rather than jurisdiction.

By this time, it has become rather common for our reviewing courts to say what we have previously stated, i.e., that "[t]he waiver rule is one of administrative convenience rather than jurisdiction" ( People v. Smith (1985), 106 Ill.2d 327, 333, 478 N.E.2d 357, 360; accord Leone v. City of Chicago (1993), 156 Ill.2d 33, 41, 619 N.E.2d 119, 123 (Miller, C.J., dissenting); People v. Burson (1957), 11 Ill.2d 360, 143 N.E.2d 239; People v. Torres (1993), 252 Ill. App.3d 567, 623 N.E.2d 1029; People v. Hayes (1977), 54 Ill. App.3d 617, 370 N.E.2d 68), a legal principle which has no counterpart in the Federal court system. It has been recognized in this State that the waiver rule is addressed only to the parties and serves to warn them that, except in limited instances, if they fail to properly preserve an issue, they are not entitled to appellate review of it. ( People v. Lowe (1992), 153 Ill.2d 195, 606 N.E.2d 1170; see also People v. Walsh (1981), 101 Ill. App.3d 1146, 1149, 428 N.E.2d 937, 940 ("The waiver rule, however, is not a limitation upon the reviewing court but an admonition to the parties").) This view of waiver explains the "plain error rule" quotation taken by the dissent from People v. Precup (1978), 73 Ill.2d 7, 382 N.E.2d 227.

People v. Jaffe (1986), 145 Ill. App.3d 840, 859, 493 N.E.2d 600. Our case can be distinguished from People v. Walsh (1981), 101 Ill. App.3d 1146, 428 N.E.2d 937, wherein the sentence was patently contrary to law because the trial court imposed an extended-term sentence for an offense that was not the most severe crime for which the defendant was convicted, in violation of the law as stated in People v. Evans (1981), 87 Ill.2d 77, 429 N.E.2d 520. In the instant case Poole's objection is that his prior conviction was not demonstrated with sufficient competent evidence.

) In People v. Walsh (1981), 101 Ill. App.3d 1146, 1149-50, 428 N.E.2d 937, the appellate court, in applying section 5-8-2(a), vacated a defendant's extended sentence because it did not belong to the class of the most serious offense of which the defendant was convicted. (Ill. Rev. Stat. 1981, ch. 38, par. 1005-8-2(a).)

(See, e.g., People v. Johnson (1979), 69 Ill. App.3d 248, 387 N.E.2d 388.) Moreover, the waiver rule is a limitation on the parties and not on the courts, and a reviewing court may ignore a waiver where the interests of substantial justice so require. ( People v. Walsh (1981), 101 Ill. App.3d 1146, 428 N.E.2d 937.) In the instant case, the record shows that the issue was not raised at trial or in a post-trial motion; however, since the problem was not clearly evident until sentence was imposed, we do not believe defendant should be faulted for failing to include it in his prior written post-trial motion.

This waiver issue is not raised by the State. The waiver rule is a restriction on the parties, not the court, and in the interests of a just result the merits of defendant's challenge will be considered. Hux v. Raben (1967), 38 Ill.2d 223, 225, 230 N.E.2d 831; People v. Walsh (1981), 101 Ill. App.3d 1146, 1149, 428 N.E.2d 937. • 2 Double taxation exists where both taxes are imposed for the same period of time, for the same purpose, upon the same taxpayer, and by the same taxing authority.

Rev. Stat. 1979, ch. 38, par. 1005-8-2(a); People v. Evans (1981), 87 Ill.2d 77, 429 N.E.2d 520). Although we are aware that this court has issued conflicting opinions regarding the interpretation of the statute as it applies to the permissibility of multiple extended-term sentences (see People v. Mims (1982), 111 Ill. App.3d 814, 444 N.E.2d 684; People v. Brown (1982), 104 Ill. App.3d 1110, 433 N.E.2d 1081; People v. DeSimone (1982), 108 Ill. App.3d 1015, 439 N.E.2d 1311; but see People v. Green (1983), 118 Ill. App.3d 227, 454 N.E.2d 792; People v. Rowe (1983), 115 Ill. App.3d 322, 450 N.E.2d 804; People v. Walsh (1981), 101 Ill. App.3d 1146, 428 N.E.2d 937) — and we are cognizant that this question currently awaits resolution by our supreme court — it is our belief that until such time as that court makes a contrary pronouncement thereon, we are controlled by its holding in Evans under which the imposition of an extended-term sentence upon Clay for conspiracy to commit armed robbery is improper. Therefore, we reduce the sentence of defendant Heard for conspiracy from an extended term of 15 years to a term of three years — the maximum permitted for the offense — and find that defendant Clay's 30-year extended sentence for conspiracy must likewise be reduced to three years.