When channels are in a cascade and are independent is the capacity the sum?
Let the first channel, channel A, have capacity $C_A=1-\varepsilon$ and the second channel, channel B, have capacity $C_B=1-\varphi$. Now put them in cascade, that is, first channel A then channel B. The resulting capacity of the cascaded channel will be $\text{min}(C_A, C_B)$. You can figure this out by thinking about the information flow like water through pipes. For example, if you're able to push $X$ bits through channel A but only $X-10$ bits through channel B, well then the total capacity will be limited by the smallest capacity channel in the cascaded system. Hope this helps!