Functus officio  Functus officio refers to an officer or agency whose mandate has expired, due to either the arrival of an expiry date or an agency having accomplished the purpose for which it was created. When used to describe a court, it can refer to one whose duty or authority has come to an end: "Once a court has passed a valid sentence after a lawful hearing, it becomes "functus officio" and cannot reopen the case." Functus officio is thus bound up with the doctrine of res judicata, which prevents the re-opening of a matter before the same court, tribunal or other statutory actor which rendered the final decision in the absence of statutory authority. There are many exceptions; for instance, where a statute authorizes variations of the original decision, the decision maker may revisit his or her previous decision. Common examples include legal competency hearings, parole board hearings and family law proceedings. There is an important difference between "res judicata" and "functus officio": the former refers to the end of a case, while the latter refers to the expiration of an office. "Functus officio" derives from "fungere": to perform, end or expire. It is cognate to the ordinary English word "defunct". "Res judicata" means "the thing has been decided" and derives from the principle "interest reipublicae ut sit finis litium" (it is for the good of the commonwealth that there be a terminus to litigation). Canadian doctrinal and judicial writing on "functus officio" is sparse, even though the rule itself derives from a 19th century case of the English Court of Appeal (In re St. Nazaire Co. (1879), 12 Ch. D. 88). Essentially, the rule holds that the court has no jurisdiction to reopen or amend a final decision, except in two cases: (1) where there has been a slip in drawing up the judgment, or (2) where there has been error in expressing the manifest intention of the court. More recently, this Court affirmed that the rule need not always be rigidly applied to tribunals in the administrative law context when the policy reasons for it are not present. In the Canadian case of "Chandler v Alberta Association of Architects", Sopinka J. wrote in relation to the principle of "functus officio": "The general rule (is) that a final decision of a court cannot be reopened ... the rule applied only after the formal judgment had been drawn up, issued and entered, and was subject to two exceptions: where there had been a slip in drawing it up, and where there was an error in expressing the manifest intention of the court."