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Topic: Getting an element of a disjoint set?
Replies: 3   Last Post: Feb 11, 2014 11:33 AM

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Victor Porton

Posts: 621
Registered: 8/1/05
Getting an element of a disjoint set?
Posted: Feb 9, 2014 10:58 AM
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Suppose I have disjoint union of sets A and B.

I want to access a particular element of this disjoint union. (For example I
need to check whether an given element is of A or of B.)

What is a good informal notation for this?

Computer proof assistants use data structures to represent disjoint union,
with symbolic field names (like structures in programming languages). But in
informal mathematics (following ZFC pattern) using identifiers is not
customary. Instead they refer to element 0 for A and 1 for B. This is not
aligned well with human perception and intuition.

How would you advise to denote this? (without going too formal)

Victor Porton -

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