Negating a Universal Statement in Real Analysis

  • Thread starter bguidinger
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In summary, the conversation discusses how to take the negation of a statement involving a Cauchy sequence in the sup norm topology. The first thought is to move the negation inside the brackets by replacing \forall with \exists and changing the sign of the inequality. The second thought is to move \varepsilon > 0 to the end of the statement. The final solution is (\exists \varepsilon>0)(\forall N \in N)(\exists n,m\geq N)(\exists x \in R [|f_n(x)-f_m(x)| \geq \varepsilon].
  • #1
bguidinger
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I am stuck in trying to take the negation of this statement:

[tex](\forall \varepsilon>0)(\exists N \in N)(\forall n,m\geq N)(\forall x \in R [|f_n(x)-f_m(x)|< \varepsilon][/tex]

One of my thoughts was that in order to move the negation inside the brackets, all I need to do is say [tex](\exists \varepsilon \leq 0)[/tex]...and everything else remains unchanged.

However, my other thought was to somehow move the statement [tex]\varepsilon > 0[/tex] to the end of the original statement and make it: [tex](\varepsilon > 0 \Rightarrow |f_n(x)-f_m(x)|< \varepsilon)[/tex]

If you can help me in anyway, it would be greatly appreciated.

Thanks!
 
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  • #2
It seems like you need something like there exists an eps >0 for which there is no N for the property (a Cauchy sequence in the sup norm topology).
 
  • #3
I figured it out...here is the solution for anyone who is curious.

[tex](\exists \varepsilon>0)(\forall N \in N)(\exists n,m\geq N)(\exists x \in R [|f_n(x)-f_m(x)| \geq \varepsilon][/tex]

Thanks for the help!
 

Related to Negating a Universal Statement in Real Analysis

What does "negation of this statement" mean?

The negation of a statement is when the opposite meaning of the original statement is expressed. It is denoted by the symbol "~" or "not".

How do you write the negation of a statement?

The negation of a statement is written by adding the symbol "~" or "not" in front of the original statement. For example, if the original statement is "I am happy", the negation would be "~I am happy" or "I am not happy".

What is the purpose of using negation in scientific research?

Negation is used in scientific research to explore all possible outcomes and to consider alternative explanations. It helps to challenge existing theories and to develop new ones.

Can a statement and its negation both be true?

No, a statement and its negation cannot both be true. They represent opposite meanings and only one of them can be true at a time.

What is the difference between negation and contradiction?

Negation is the opposite of a statement, while contradiction is a statement that is false in all circumstances. Negation can still be true in certain circumstances, while contradiction is always false.

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