admitting that "common sense and fair play" would extend this duty to all inventions. Some authors such as Professor Vaver argue that this revisionism seems wrong given prior case law and the Supreme Court of Canada's decision in Consolboard Inc. v. MacMillan Bloedel (Saskatchewan) Ltd. which recognized that the Act's disclosure provision is badly drafted and cannot be read literally. The claims The claims are a mandatory part of the specification through s. 27(4) of the Patent Act which states: Thus, the claims require the patent applicant to stake out the monopoly sought. Claims are sometimes analogized as a series of "fences" surrounding and protecting the valuable invention. Anything outside the fence is public domain: "what is not claimed is disclaimed." Since each claim is an independent grant of monopoly, one or more may be found invalid without necessarily affecting the validity of any other. This system leads inevitably to inventors claiming the broadest interpretation possible of what their invention is, and progressively claim narrower variations. In order to determine whether a claim is infringed or invalid, the Court will read the claims and give them a meaning through a process referred to as "claim construction". As Professor Vaver explains, trying to estimate the outcome of claim construction is next to impossible: Thus, the game for patent holders is to reveal as little as possible, while claiming as much as possible. The less that is disclosed, the more that can be retained and serve as a competitive edge. The wider the claims, the tougher it is for competitors not to infringe, however, the patent holder must avoid the known and the obvious or risk patent invalidity. The abstract The abstract section summarizes the invention’s purpose. The abstract should describe the technical problem and the solution of the problem by the invention in a succinct way so that a reader can decide whether the rest of the patent is of interest. Unity of invention The general rule is "one invention, one application, one patent". However, multiple claims covering all facets are allowed in the same patent if a "single inventive concept" links them. If more than one invention is disclosed, the application can be split into two or more "divisional applications", each claiming the requisite one invention. One invention does not become two inventions just because it is contained in another product. Professor Vaver provides the following example to illustrate the