As an example, let's look at the set of numbers from 1 to 5. Let's suppose there were a function f which maps each member onto a subset. It might map 1 onto {1,3,4}. This contains 1. It might map 2 onto {1,5}. This doesn't. That's the gist of the line you're looking at.
The next step is to say 'let's look at the numbers like 2 in the example which don't go to subsets with them in'. Make a subset of those numbers. What number could map to it? It can't be one in the subset because of the definition of the subset, but it can't not be in the subset because then it fulfils the criteria for being in it.
This is a lengthier version: here
I hope this helps.
The next step is to say 'let's look at the numbers like 2 in the example which don't go to subsets with them in'. Make a subset of those numbers. What number could map to it? It can't be one in the subset because of the definition of the subset, but it can't not be in the subset because then it fulfils the criteria for being in it.
This is a lengthier version: here
I hope this helps.
