I am learning interval notation. One of my friends said that besides from '('and '[',there is '{'. Is it true? Is there any " { or }"in interval notation? If yes, what is it used for?

Question

Thank you so much :-)

Answer 1

Yes, you can use {} to describe an interval, but it is not part of the interval notation.

The use of {} is used to define a set which gives the same members as the interval notation, for example:
(4,7)=]4,7[={x|4<x<7}
The right hand side of the equal sign defines a set where the members are real numbers between 4 and 7, excluding 4 and 7.

Answer 2

I don't get your example and the use of { }, can you explain further?
Thank You =]

Answer 3

(4,7) is the normal interval notation indication all real numbers between 4 and 7 but excluding 4 and 7.
It can also be written as ]4,7[.
[4,7] is the interval notation also for including all real numbers between 4 and 7 but including the two limits, namely 4 and 7.
{x|4<x<7} is a set notation to define a set of real numbers between 4 and 7 and excluding 4 and 7. Another example of the set notation is
{4,5,6,7} for the set of four integers from 4 to 7.
In short, you can also define an interval using the set notation, but it is ot part of the intervl notation.2

Answer 4

OK. Thanks. =]