Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I just started learning set theory.I have a question I need to answer for revision. I missed a bit of my lecture so i'm a little lost and I have yet to receive my textbook.

The question is: "Write [–3..1] as a set by explicitly listing all its elements. "

Just wondering how that works?

share|improve this question
4  
My gut reaction would be that this is impossible because $[-3,1]$ represents the set of all real numbers $x$ such that $-3\leq x\leq 1$. The fact that you are asked to do it, though, suggests to me that this is some special notation introduced in your course, possibly the set of all integers between $-3$ and $1$. If so, I would point out that I would "explicitly list" the set $[5..8]$ like so: $\{5,6,7,8\}$. –  Arturo Magidin Aug 17 '11 at 21:03
    
Thanks, I'll have to ask the professor. :) –  jojoi Aug 17 '11 at 21:17
    
@Arturo: $\{x\in\mathbb R\mid -3\le x\le 1\}$ is not explicit, I take it? –  Asaf Karagila Aug 17 '11 at 22:24
    
@Arturo Magidin: Note that the OP wrote $[-3..1]$, not $[-3,1]$. –  Ben Crowell Aug 18 '11 at 2:22
    
@Asaf: It's not a way of "explicitly listing all the elements", no. –  Arturo Magidin Aug 18 '11 at 3:11
show 1 more comment

1 Answer 1

If $n$ and $m$ are integers with $n\le m$, the two-dots notation $[n..m]$ commonly denotes the set of integers between $n$ and $m$ inclusive: $[n..m] = \{k \in \mathbb{Z}:n \le k \le m\}$. If that’s the convention that your class is using $-$ and it’s common in computer science, so it’s not unusual in discrete math courses $-$ then $[-3..1] = \{-3,-2,-1,0,1\}$.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.