you're allowed to assume perfect efficiency, unless you can show it to be physically impossible Even then, his specification is at too high a level of abstract

you're allowed to assume perfect efficiency, unless you can show it to be physically impossible Even then, his specification is at too high a level of abstraction for us to prove that it's physically impossible. That seems unfair. If the author wants people to ignore the abstractions that quickly prove something impossible, then he or she should provide enough detail to analyze it from a practical perspective.