  The paper presents a simple derivation of the Gustafson-Barsis law from the
Amdahl's law. In the computer literature these two laws describing the speedup
limits of parallel applications are derived separately. It is shown, that
treating the time of the execution of the sequential part of the application as
a constant, in few lines the Gustafson-Barsis law can be obtained from the
Amdahl's law and that the popular claim, that Gustafson-Barsis law overthrows
Amdahl's law is a mistake.
