# Clarify the steps: what happened in this mathematical modeling of the TSP?

Source: http://examples.gurobi.com/traveling-salesman-problem

I do not understand this part: (look at the source)

I understand that $$x_ {ij}$$ is equal to 3 but why the “> 2 "?

And what's the problem with subtracting 1 from a set? How do you even do that?

How to come $$| {1,2,3 } | -1 = 3> 2$$ ?!

Good then:
$$| {1,2,3 } | -1 = 2$$

So, how is he allowed to write:
$$| {1,2,3 } | -1 = 3> 2$$

?

It's basically the same thing as writing: (which is incorrect, right?) $$2 = 3> 2$$

I do not understand this part at all, please explain what happened in language as simple as possible. My level is the final math level of high school.