Either/or diagramming is actually quite simple. You'll get the hang of it in no time. We know we are in an either/or situation when we are limited to two options. I'll give you an example.
I'm either going to the store, or I'm going to the library. (One of these things must occur, and it is possible for both of them to occur, unless otherwise specified.) When we have two options, and one of them does not occur, we know that the other one did occur.
Therefore, if I'm not going to the store, then I'm going to the library. not S - - - - - - - > L If I'm not going to the library, then I'm going to the store. not L - - - - - - - -> S
However, as Mehran specified in the video, if I do go to the store, we cannot make a conclusion about whether or not I go to the library, and vice versa. Unless it says "not both," it is possible to have both.
