MHB How have we concluded that X is an inductive set?

  • Thread starter Thread starter evinda
  • Start date Start date
  • Tags Tags
    Set
evinda
Gold Member
MHB
Messages
3,741
Reaction score
0
Hello! (Nerd)

I am looking at the proof of the following sentence:

For any natural numbers $m,n$ it holds that:

$$n \in m \rightarrow n \subset m$$

Proof:

We define the set $X=\{ n \in \omega: \forall m (m \in n \rightarrow m \subset n)$ and it suffices to show that $X$ is an inductive set.
Then, $\varnothing \in X$.
Let $n \in X$.
We want to show that $n'=n \cup \{ n \} \in X$.
We pick a $m \in n'=n \cup \{ n \}$.
Then $m \in n$ or $m \in \{ n \}$.
  • If $m \in n$ and since $n \in X$, we have that $m \subset n$
  • If $m \in \{ n \} \rightarrow m=n \rightarrow m \subset n$

So, $n' \in X$ and therefore $X$ is an inductive set.I haven't understood why, having shown that $m \subset n$, we have concluded that $n' \in X$. (Worried)
Could you explain it to me? (Thinking)
 
Physics news on Phys.org
In order to show that $n' \in X$ don't we have to show that $m \in n' \rightarrow m \subset n'$ ? Or am I wrong? (Thinking)
 
In both cases in the proof, we have $m\subseteq n$. This trivially implies $m\subseteq n'$.
 
Evgeny.Makarov said:
In both cases in the proof, we have $m\subseteq n$. This trivially implies $m\subseteq n'$.

I see (Nod) Thank you very much! (Happy)
 
Hi all, I've been a roulette player for more than 10 years (although I took time off here and there) and it's only now that I'm trying to understand the physics of the game. Basically my strategy in roulette is to divide the wheel roughly into two halves (let's call them A and B). My theory is that in roulette there will invariably be variance. In other words, if A comes up 5 times in a row, B will be due to come up soon. However I have been proven wrong many times, and I have seen some...
Thread 'Detail of Diagonalization Lemma'
The following is more or less taken from page 6 of C. Smorynski's "Self-Reference and Modal Logic". (Springer, 1985) (I couldn't get raised brackets to indicate codification (Gödel numbering), so I use a box. The overline is assigning a name. The detail I would like clarification on is in the second step in the last line, where we have an m-overlined, and we substitute the expression for m. Are we saying that the name of a coded term is the same as the coded term? Thanks in advance.

Similar threads

Replies
5
Views
1K
Replies
2
Views
2K
Replies
30
Views
5K
Replies
6
Views
2K
Replies
8
Views
2K
Back
Top