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I am trying to brush up on some mathematics and realized that I have to start from the very bottom. I keep getting confused by the symbols and it has been an ardeous last few days!

Anyway, going through some stuff on set theory and came across the concept of equivalance classes. Let me see if I have understood this correctly:

If we have an equivalant relation on elements a and b of a set, than the set of all elements that are equivalant to a would be the equivalant class of element a. Does that sound right? I have a feeling I have understood it all wrong also because I am finding it hard to get used to the notations.

Then it goes on to say that if there is an equivalance relation on A and a, b are elements of set A, then either

[[a]] union [] = null set or [[a]] = []

This is not immediately obvious to me and I would be really grateful if someone can shed some light on this.

I would be grateful for any help you can give this old man :)

/Luca

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# Basic quesion about equivalance classes

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