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**Reuel****Member**- Registered: 2010-11-28
- Posts: 178

Hi!

I don't know a lot about sets or set notation but I have taught myself the basics. I was wondering if anyone could please tell me how to formally make the statement that the members of two sets directly correspond with each other.

For instance, if we have two arbitrary sets

and we wish to make the statement that 0 corresponds with a, 1 corresponds with b, etc., how would we go about doing that?

Also, they are not the same set. A real world example might be moments in time and events in time where each event occurs in each moment. What would be the formal mathematical expression?

Thanks!

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,979

I'd do it like this:

The backwards E stands for "there exists".

A bijection is a relationship that is 1 to 1 between the sets.

http://www.mathsisfun.com/sets/injectiv … ctive.html

http://en.wikipedia.org/wiki/Bijection

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**Reuel****Member**- Registered: 2010-11-28
- Posts: 178

Thank you! That is exactly what I was looking for.

*Last edited by Reuel (2013-10-18 00:48:48)*

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**Reuel****Member**- Registered: 2010-11-28
- Posts: 178

In the same fashion, if we have a number line made up of all the real numbers and if there is a boundary within

how do we say that we want to have the set of everything from a to b in terms of all reals minus everything except for what is in the set from a to b? I understand the set from a to b is a subset of all reals but how can it be defined as the set of all reals minus everything except what exists within the set a->b?

On a related note, does anyone know of a good web site or book that teaches all about set notations? I checked out Khan Academy but there were only a few videos on the basics.

Thanks.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

You, mean

*Last edited by anonimnystefy (2013-10-18 01:42:44)*

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**Reuel****Member**- Registered: 2010-11-28
- Posts: 178

Yes, thank you.

Are there any good books on set notation? I want to learn to write more formally in mathematics but the web sites I have looked at thus far are not so great.

Thanks again.

Actually you probably meant

but I knew what you meant.

*Last edited by Reuel (2013-10-18 02:17:14)*

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**Reuel****Member**- Registered: 2010-11-28
- Posts: 178

Okay, here is what I have. I would appreciate any edits or suggestions anyone who knows sets or mathematical writings might have to offer to help improve the quality of what I have so far.

---

If time is initially defined as a well-ordered uncountable set

[in that it might be said to go from ±∞], the set T might be written so as to contain some boundary condition

so that it can be rewritten as

;but if we further define the set as being of certain relevance to *only* that boundary condition Z, we say let

so as to be redefined as

.Suppose then we have a series of events in time that are also restricted to Z (which is actually what I intend to be the reason for why Z is a boundary condition in the first place) and let that ordered set (ordered because it corresponds to time T) be given by

.Because every event in E corresponds to no more and no less than one event in T,

(meant to read: a function t is the mapping of the set E to the set T such that for all t's in the set T there exists one and only one e in E such that t as a function of e is equal to t)

such that for a bijector J between T and E,

so that

and

that is, the cardinality of both sets is equal such that the magnitude of both sets is equal:

.---

Thank you for any and all input. Any and all critiques and edits are welcome.

P. S. Yes, starting out with the most fundamental definition of time is a goal, then to be worked out so as to be limited to the specified boundary condition which is so-bounded because of the set of E being the only set where T is relevant.

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**Reuel****Member**- Registered: 2010-11-28
- Posts: 178

As there are no replies I will assume there are no outrageous errors, except I think maybe I should have written

with the factorial if I wanted to say "there exists one and only one".

Thanks for the help, guys.

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