The majority would reverse the judgment of the Court of Appeal and remand the matter to the trial court to permit defendant to make an allegation that he was prejudiced by the trial court’s failure to advise him accurately of the parole consequences of his guilty plea. There is no need for such a remand; the allegation was supplied in the trial court by the People’s concession that defendant was entitled to relief. Our remand is a waste of judicial resources.
There is also no basis for a remand to the trial court to determine whether the sentence imposed was a violation of the plea agreement: the People conceded the issue. I would affirm the judgment of the Court of Appeal directing that no more than a five-year term of parole be imposed on defendant.
I
The trial court informed defendant at the time of entry of the guilty plea, and again at sentencing, that he was subject to a term of fifteen years to life *359in prison, with parole for a period of either three or four years. After the finality of the judgment, defendant filed a petition for writ of habeas corpus alleging that the court had failed to advise him the guilty plea to a charge of second degree murder actually subjected him to lifetime parole, and that the imposition of a lifetime parole term would violate the plea bargain. Defendant contended that he should be permitted to withdraw his guilty plea.
It is true that defendant’s petition for writ of habeas corpus failed to make the allegation that he would not have entered the guilty plea if he had been informed that he would be subject to lifetime parole. It is also true that such an allegation is generally required in order to make out a claim for relief on habeas corpus for a court’s failure to advise a defendant of the consequences of a guilty plea. (In re Ronald E. (1977) 19 Cal.3d 315, 325-326 [137 Cal.Rptr. 781, 562 P.2d 684].)
However, the People’s pleadings and arguments in this case supplied the missing allegation by conceding defendant’s entitlement to relief.
The same deputy attorney general who appeared before us in this court stated in the return to the order to show cause and also in the points and authorities in support of the return: “For the reasons set forth above, respondent agrees that an error was committed by the trial court, but disagrees that the appropriate remedy is to permit petitioner to withdraw his plea. Respondent respectfully requests that this court order specific performance of the plea bargain to which all parties agreed at the time of sentencing.” (Italics added.)
Defendant obviously relied on this statement. His “denial” to the return declares that “[t]he sole issue before the court is the remedy which should be directed. Petitioner alleges that he should be allowed to withdraw his plea. Respondent argues for specific enforcement by way of reducing petitioner’s parole period to the term he was advised of by the sentencing court.”
At the hearing on the order to show cause, the People again conceded that defendant was entitled to relief because of the trial court’s serious error in advising him of the parole consequences of his plea. At the hearing, the People, now represented by the Humboldt County District Attorney’s office, argued: “this is really a case [in] which the court has two options. The choice of remedy: whether the plea shall be withdrawn, or whether the Court should order specific performance of the agreement.”
The People continued: “So, we concede there is an error here and the writ is the proper remedy and vehicle to redress the wrong. [¶] It is our position *360that a withdrawal of the plea would exploit the error and not enforce the benefits of it. [¶] The state[’]s interest in this case is in preserving a conviction by providing Mr. Moser what he bargained for . . . .” (Italics added.)
In answer to defendant’s claim that the court lacked authority to impose the shorter parole term, the People offered to stipulate to that form of relief: “And I submit the Court does, under the authority of Mancheno, Flores and Oberreuter particularly when both the District Attorney, the Attorney General and Board of Prison Terms are essentially parties to this action and indicate we are willing to stipulate to a reduced parole period. This is really an extraordinary commitment by the Board of Prison Terms, [¶] The Attorney General and our office say yes, there was misadvice there. Mr. Moser should get the benefit of that misadvice and that has been limited to a three year period of parole.” The deputy district attorney pursued the point: “This state has an interest in preserving the conviction. We will benefit from a reduced parole period, and we have agreed to accept that term. We believe strongly there can be no error or prejudice in specifically enforcing that term.” (Italics added.)
In rebutting defendant’s claim that he was entitled to withdraw his plea, the People said: “[Counsel’s] argument might have weight if the Board of Prison Terms or Attorney General were contesting the ability of this Court to so order three year term .... The Court has two choices, either withdraw the plea or specific enhancement [sic]. There would be no prejudice or appeal from the Board nor from the Attorney General should the Court so order.’’'’ (Italics added.)
In their appeal from the order permitting defendant to withdraw his guilty plea, the People did not contend that defendant was not entitled to relief because he had failed to allege prejudice. The issue was never raised. The People did argue on appeal that the petition for writ of habeas corpus had been untimely, but declared: “This case is less a case of inadequate admonition than a plea bargain in need of specific performance guarantees. As we demonstrate below, since respondent has not yet been released on parole, this court can insure that he gets the sentence for which he bargained, simply by ordering that his parole term, if any, be set at the fixed term imposed by the trial court. The Board of Prison Terms has agreed to this procedure. [¶] Neither an appellate court nor any court hearing a petition for writ of habeas corpus is restricted to the remedy of reversal when prejudicial error is found.” (Italics added.)
The People maintained that a reduced parole term was the proper remedy, and concluded: “Accordingly, for the reasons stated, appellant respectfully *361asks that the order granting respondent’s petition for writ of habeas corpus be reversed and, if the issue is reached on the merits, the People’s offer of specific performance accepted.” This same conclusion was repeated in the People’s reply brief. As the People did not argue that defendant had failed to show prejudice, it is understandable that the Court of Appeal said nothing about defendant’s failure to allege he would not have entered the plea if he had known he was subject to lifetime parole. Therefore that nonexistent issue should not detain us.
It seems patently clear that when the People conceded defendant’s entitlement to relief in their return and at the hearing on the order to show cause, they necessarily conceded prejudice. “In a habeas corpus proceeding the return to the order to show cause must allege facts tending to establish the legality of the petitioner’s detention; it is thus analogous to the complaint in civil actions. The traverse, which may incorporate the allegations of the petition, is analogous to the answer in civil actions. [Citations.] It is in this manner that the factual and legal issues are joined for review.” (In re Sixto (1989) 48 Cal.3d 1247, 1252 [259 Cal.Rptr. 491, 774 P.2d 164].) Under this standard, it is impossible to understand how the issue of prejudice could be open on appeal, when the People conceded it below. The People’s concession that defendant was entitled to relief should have limited the issues on review to the question of defining the appropriate relief. The trial court selected the remedy against which the People argued, but the People’s appeal from this decision should not be considered to reopen the basic question of entitlement to relief.
Justice in this case requires the People to be held to their forthright concession in the trial court that the appropriate remedy in this matter is to reduce defendant’s parole term.
II
A negotiated guilty plea requires both parties to honor the agreement as to sentence. (People v. Walker (1991) 54 Cal.3d 1013, 1024 [1 Cal.Rptr.2d 902, 819 P.2d 861].) As a matter of due process, “[t]he punishment may not significantly exceed that which the parties agreed upon.” (Ibid.)
In response to defendant’s claim that the imposition of lifetime parole would be a violation of the plea agreement, the majority seem to say that unless the parole term was an express inducement to the plea, in the sense that the defendant can show on remand that he actually discussed it and relied on it in making the decision to enter the guilty plea, defendant is entitled to no relief at all—not even specific performance of the ultimate bargain. (Maj. opn., ante, pp. 355-356, 357.)
*362I disagree. A significant new term of punishment may not be added to the sentence ex post facto on the theory that because it was not a precise subject of negotiation, its absence was not a term of the negotiated plea. To permit an expanded term of punishment to be added on such a unique theory would be comparable to permitting a party to a contract to demand additional consideration after the fact for fulfillment of the bargain because the absence of that precise term was not discussed during negotiation or noted in the terms of the contract. Simple contract principles forbid such a result. (See People v. McClellan, post, pp. 367, 382-383 [24 Cal.Rptr.2d 739, 862 P.2d 739] (conc. & dis. opn. of Mosk, J.).)
As the majority concede, defendant is not required to establish he would not have entered the plea if he had known of the lifetime parole term in order to claim a violation of the bargain. (People v. Walker, supra, 54 Cal.3d at p. 1026.) He need only show that the court proposes to add a significant term of punishment to the bargained-for term. (Ibid.) “A court may not impose punishment significantly greater than that bargained for by finding the defendant would have agreed to the greater punishment had it been made a part of the plea offer. ‘Because a court can only speculate why a defendant would negotiate for a particular term of a bargain, implementation should not be contingent on others’ assessment of the value of the term to defendant. . . .’” (Ibid.)
Defendant did not bargain for lifetime parole, and the addition of such a term is obviously significant. “Courts should generally be cautious about deeming nonbargained punishment to be insignificant. The test whether a punishment greater than that bargained for is ‘significant’ under Santobello v. New York [(1971)] 404 U.S. 257 [30 L.Ed.2d 427, 92 S.Ct. 495] is stricter than the prejudice test for a mere failure to advise of the consequences of a nonbargained plea. Punishment that is not prejudicial, i.e., when it is not reasonably probable the defendant would not have pleaded guilty if informed of the punishment. . . may well be ‘significant’ if imposed after a negotiated plea.” (People v. Walker, supra, 54 Cal.3d 1013, 1028, fn. 3.)
In People v. Walker, supra, 54 Cal.3d 1013, the defendant was advised that he might be subject to a penalty fine of $10,000, but not that he was subject to a mandatory restitution fine of up to $5,000. When the court imposed a $5,000 fine at sentencing, we said this was a significant deviation from the bargain. If this increase in mere financial penalty was a significant deviation in the terms of the sentence, certainly an increase in parole from three years to life necessarily is significant. This is not the type of minor addition to punishment, such as the addition of a standard term of probation supervision, that we can overlook as insubstantial. (See Santobello v. New York (1971) 404 U.S. 257, 262 [30 L.Ed.2d 427, 433, 92 S.Ct. 495].)
*363The majority suggest that a “mere misadvisement” regarding the parole consequences of a plea would never be significant enough to be considered a violation of a plea agreement. (Maj. opn., ante, p. 354.) They rely on United States v. Timmreck (1979) 441 U.S. 780, 784 [60 L.Ed.2d 634, 638-639, 99 S.Ct. 2085], which held that a technical violation of rule 11 of the Federal Rules of Criminal Procedure (18 U.S.C.) regarding advising defendant of the parole consequences of his plea did not provide a basis for relief on habeas corpus. But that case did not present the issue of a violation of a plea agreement; it did not cite Santobello v. New York, supra, 404 U.S. 257, or analyze a due process claim such as that raised in this case. These omissions are not surprising, because the case did not involve a sentence bargain. (See Carter v. McCarthy (9th Cir. 1986) 806 F.2d 1373, 1377, fn. 4 [affirming relief on habeas corpus in part because the addition of a mandatory parole term not mentioned at the time of the plea exceeded the sentence defendant had been promised].) It is axiomatic that cases are not authority for propositions not considered.
That it would be a significant deviation from the agreed punishment to impose lifetime parole is clear from the forthright posture of the People below conceding defendant was entitled to relief from this deviation from the plea agreement, and arguing in favor of a reduction of the parole term. In fact, as I have noted, both the People and the Board of Prison Terms on behalf of the State of California offered to stipulate to a reduction in defendant’s parole term. Justice demands we affirm the decision of the Court of Appeal granting defendant relief from a significant punishment for which he and the People did not bargain.