In Evans v. Board of Probation and Parole, 820 A.2d 904, 914-15 (Pa. Cmwlth. 2003), the petitioner filed for a writ of mandamus alleging, among other issues, that the Pennsylvania Board of Probation and Parole (Parole Board), erred in retroactively applying Section 9718.1 of the Sentencing Code to him in violation of the ex post facto clauses of the United States and Pennsylvania Constitutions, and in denying his parole because of his failure to participate in programs that petitioner averred were established as "voluntary." As in the matter sub judice, the respondent in Evans filed preliminary objections to the petition for writ of mandamus, and the Evans Court restated the following requisite guidelines regarding writs of mandamus and preliminary objections thereto: A writ of mandamus is an extraordinary remedy designed to compel official performance of a ministerial act or mandatory duty. McGill v. Pennsylvania Department of Health, Office of Drug and Alcohol Programs, 758 A.2d 268, 270 (Pa. Cmwlth. 2000). Thus, in an action in mandamus involving an administrative agency's exercise of discretion, we may only direct the agency to perform the discretionary act; we may not direct the agency to exercise its judgment or discretion in a particular way or direct the retraction or reversal of action already taken. Id. A writ of mandamus may be issued only where there is a clear legal right in the plaintiff, a corresponding duty in the defendant, and lack of any other appropriate and adequate remedy. Id. The purpose of mandamus is not to establish legal rights, but to enforce those rights already established. Id. at 914-15 (Pa. Cmwlth. 2003). In ruling upon a preliminary objection in the nature of a demurrer, we must accept as true all well-pleaded allegations of material fact and all inferences reasonably deductible therefrom. Myers v. Ridge, 712 A.2d 791, 794 (Pa. Cmwlth. 1998). The Court need not accept as true conclusions of law, unwarranted inferences, argumentative allegations, or expressions of opinion. Id. The test is whether it is clear from all of the facts pleaded that the pleader will be unable to prove facts legally sufficient to establish his or her right to relief.Id. at 906 n.3. In Evans, the Court rejected petitioner's arguments based upon the following: (1) petitioner failed to prove that Act 2000-98 (adding 42 Pa.C.S. 9718.1) on its face or as applied to him, created a significant, not a speculative or attenuated, risk of increasing the severity of his punishment, a critical issue addressed in California Department of Corrections v. Morales, 514 U.S. 499, 115 S. Ct. 1597, 131 L. Ed. 2d 588 (1995) and in Garner v. Jones, 529 U.S. 244, 120 S. Ct. 1362, 146 L. Ed. 2d 236 (2000); (2) assuming arguendo that Act 2000-98 was retroactively applied, it still does not on its face violate the ex post facto clause because the Act's mandatory provisions apply only to "offenses committed on or after the effective date of this act;" Id. at 911. (3) Act 2000-98 permits but does not mandate "consideration of the Act's factors in granting or denying parole for offenses committed before the effective date of this act," and does not undermine the Parole Board's discretion to consider whether a state inmate who committed a sexual offense involving a minor before Act 2000-98 was passed should receive sex offenders' treatment; Id. (4) Act 2000-98 was not intended to function as a "penal" statute, but rather to protect the public by providing treatment to an offender before his release into society; (5) petitioner did not have a liberty interest in the expectation of release on parole prior to the expiration of his maximum sentence, and therefore did not establish a due process violation; and (6) petitioner's attempt to file a writ of mandamus to challenge the Parole Board's denial of parole must fail considering that the grant or denial of parole is solely within the Parole Board's discretion.