What is the test for prior disclosure in a patent application?

He explains that the requirement of prior disclosure means that the prior patent must disclose subject matter which, if performed, would necessarily result in infringement of that patent, and states, at para. 22: If I may summarise the effect of these two well-known statements [from General Tire and Hills v. Evans], the matter relied upon as prior art must disclose subject matter which, if performed, would necessarily result in an infringement of the patent. . . . It follows that, whether or not it would be apparent to anyone at the time, whenever subject matter described in the prior disclosure is capable of being performed and is such that, if performed, it must result in the patent being infringed, the disclosure condition is satisfied. When considering the role of the person skilled in the art in respect of disclosure, the skilled person is “taken to be trying to understand what the author of the description [in the prior patent] meant” (para. 32). At this stage, there is no room for trial and error or experimentation by the skilled person. He is simply reading the prior patent for the purposes of understanding it.