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With reference to the question, posted by me at Stackoverflow here, i want to know the mathematical details about the concept.

Below is my question.

In multiple set, which contains Integers, I want to get all those elements, which has no duplicate. i.e. which came only once in union of all the Set. Ex: consider set first contains {2,4,6,8,9}, second set contains {2,8,9} and third set contains {2,4,8,9}. In all these sets, element 6 occurs only once.

Somebody please explain the set theory behind it.

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I'm not sure what is the question, but I am fairly certain that it's not set theory. I have tagged it as elementary set theory, but I'm not 100% convinced that it fits either. Someone else who understands what is asked here please retag or confirm my retag. Thanks. –  Asaf Karagila Dec 8 '12 at 14:58
    
@AsafKaragila: Hey, it is elementary set theory only. Basic set theory operations may help. But don't know how :( –  Ravi Joshi Dec 8 '12 at 15:01
    
The word "intersection" comes to mind. –  Asaf Karagila Dec 8 '12 at 17:14

2 Answers 2

Here's what I see in the question:

  1. Union of the 3 sets: U = {2,4,6,8,9}
  2. A counter -function which counts how many times each number is used: $$f : U\rightarrow N,$$ $$f = \{2\rightarrow 3, 4 \rightarrow 2, 6 \rightarrow 1, 8 \rightarrow 3, 9\rightarrow 3\}$$
  3. An equation which chooses the elements where count is one: f(X)=1.
  4. The resulting set: X = {6}
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I think you have it right, but in step 2 the function could just return 1 or "more than 1". I don't know if that makes it easier. –  Ross Millikan Dec 8 '12 at 16:54

The set theory formulation of your problem would be to let $A_i$ be your input sets. Let $\phi(x)=\exists i \exists j (i \neq j \wedge x \in A_i \wedge x \in A_j)$ Then your output is the set $\{y | y \in \bigcup A_i \wedge \lnot \phi(y)\}$. I'm not sure this explains anything.

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