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Math Help - set builder problem

  1. #1
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    set builder problem

    i cant figure out if how to write this in set builder notation
    {{0},{0,1},{0,1,2},{0,1,2,3}.....} can anyone help me with this i guessed that you could do it like this
    {x | for all x there is a value y that is y < x i and y and x are positive integers}
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  2. #2
    Senior Member Dinkydoe's Avatar
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    There's probably a few ways to do it, I'd say:

    \left\{u\in \mathcal{P}(\mathbb{N}): x\in u \wedge y< x\rightarrow y\in u \right\}

    I think this will do it
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  3. #3
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    Quote Originally Posted by Dinkydoe View Post
    There's probably a few ways to do it, I'd say:

    \left\{u\in \mathcal{P}(\mathbb{N}): x\in u \wedge y< x\rightarrow y\in u \right\}

    I think this will do it
    Is it \left\{u\in \mathcal{P}(\mathbb{N}): (x\in u) \wedge (y< x)\rightarrow y\in u \right\}?

    (y< x) part is hard to picture.

    Can we say \{u\in \mathcal{P}(\mathbb{N}): u =[0,n] , n \in Z^{+}\}?
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  4. #4
    Senior Member Dinkydoe's Avatar
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    Is it ?
    That's true. It's the same. I believe setting these "()" is not strictly necessary, but it makes it better readible I guess

    Can we say ?
    That's a good question. Actually I'm not sure: Normally we keep the notation [a,b] as an interval in \mathbb{Q}, or \mathbb{R}.

    Anyway: I think just writing \left\{\left\{0,1,\cdots ,n\right\}: n\in \mathbb{N}\right\} Is suggestive enough in itself. Every mathematician will know what you mean ;p

    \left\{u\in \mathcal{P}(\mathbb{N}): (x\in u) \wedge (y< x)\rightarrow y\in u \right\} is a more formal notation.
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  5. #5
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    Quote Originally Posted by Dinkydoe View Post
    That's true. It's the same. I believe setting these "()" is not strictly necessary, but it makes it better readible I guess

    That's a good question. Actually I'm not sure: Normally we keep the notation [a,b] as an interval in \mathbb{Q}, or \mathbb{R}.

    Anyway: I think just writing \left\{\left\{0,1,\cdots ,n\right\}: n\in \mathbb{N}\right\} Is suggestive enough in itself. Every mathematician will know what you mean ;p

    \left\{u\in \mathcal{P}(\mathbb{N}): (x\in u) \wedge (y< x)\rightarrow y\in u \right\} is a more formal notation.
    Let's give another try:

    Is \left\{u\in \mathcal{P}(\mathbb{N}): 0\leq x\leq n, x \in u, n\in \mathbb{N} \right\} considered a formal notation?

    In this lesson, I have learned from you "Normally we keep the notation [a,b] as an interval in \mathbb{Q}, or \mathbb{R}."
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  6. #6
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    thanks for the quick replys I am still waiting for my prof to tell me the solution proved was correct here was his sugguestions prior to me posting this on the board. Im guessing this is going to be on the quiz since he wont just tell me the answer.

    ----
    What is the set { x | 0 <= x <= b } ? Isn't that the typical element of the set of sets we are trying to describe? Now just index this over all the relevant values of b, using appropriate set-builder notation.
    ----
    include all the integers from 0 to k for each fixed k. Find a way to



    >> say that using set-builder notation (you'll be using set-builder



    >> notation within set-builder notation).
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  7. #7
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    For your question, I think it's simpler to write \{A_{n \in \mathbb{N}}\}=\{\{0\},\{0,1\},\{0,1,2\},...\}, so that in set builder form

    we can write \{A_{n \in \mathbb{N}}\}, where A_n= \{a\in \mathbb{N}: 0\leq a \leq (n-1) \}.
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  8. #8
    MHF Contributor Drexel28's Avatar
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    Quote Originally Posted by novice View Post
    Is it \left\{u\in \mathcal{P}(\mathbb{N}): (x\in u) \wedge (y< x)\rightarrow y\in u \right\}?

    (y< x) part is hard to picture.

    Can we say \{u\in \mathcal{P}(\mathbb{N}): u =[0,n] , n \in Z^{+}\}?

    It is common notation to denote \left\{1,\cdots,n\right\} by either \bold{n} or [n]. Make sure you specify. Also, it is incorrectly
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  9. #9
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    Quote Originally Posted by Drexel28 View Post
    It is common notation to denote \left\{1,\cdots,n\right\} by either \bold{n} or [n]. Make sure you specify. Also, it is incorrectly
    You are right, now that I am learning theoritical math, I need to form a new habit of specifying notations.

    I am so glad you metioned the notations in quote. I have never seen them before.
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