Is this statement an aspect of the Hairy Ball or Fixed Point Theorem?

In summary, the statement is an alternate version of the axiom of choice and implies the more commonly known version. It suggests that given a set of mutually exclusive classes, there will always be at least one class that shares one term with each of the given classes, similar to the concept of a hair whorl or a crumpled bingo paper.
  • #1
swampwiz
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“Given any class of mutually exclusive classes, of which none is null, there is at least one class which has exactly one term in common with each of the given classes…”

The reason this statement sounds like one of those theora is that I recall reading a Time-Life book on Mathematics, and there was a discussion about the fact that a hair whorl always has at least 1 point where the hair doesn't whorl, and as well that if a sheet of bingo paper is crumpled up and placed on an identical un-crumpled up sheet, there will be at least 1 bingo number for which that of the crumpled one will be on top of that of the un-crimpled one, and it seemed that this was the same idea as the hair whorl.
 
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  • #2
This looks like an alternate statement of the axiom of choice: if the family of disjoint sets is ##\{E_{\alpha}\}_{\alpha\in A}## and for each ##\alpha\in A,## we select an element ##a_{\alpha}\in E_{\alpha}## [using axiom of choice here] then the set ##\bigcup_{\alpha\in A}\{a_{\alpha}\}## has exactly one element in common with each ##E_{\alpha}.##

It also implies the (usual statement of the) axiom of choice, because given the family ##\{E_{\alpha}\}_{\alpha\in A}## and such a set ##E##, then ##E\cap E_{\alpha}## selects one element from each set.
 
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FAQ: Is this statement an aspect of the Hairy Ball or Fixed Point Theorem?

What is the Hairy Ball Theorem?

The Hairy Ball Theorem is a mathematical theorem that states that it is impossible to comb a hairy ball flat without creating a cowlick or a fixed point where the hair stands up. In other words, there will always be at least one point on a hairy ball where the tangent vector is equal to zero.

What is the Fixed Point Theorem?

The Fixed Point Theorem is a mathematical theorem that states that any continuous function on a compact convex set must have at least one fixed point. In other words, there will always be at least one point in the set that the function maps to itself.

What is the relationship between the Hairy Ball and Fixed Point Theorems?

The Hairy Ball and Fixed Point Theorems are both related to the concept of fixed points. The Hairy Ball Theorem is a special case of the Fixed Point Theorem, as it applies specifically to the mapping of a hairy ball onto itself. However, the Fixed Point Theorem has a much broader application and can be applied to a variety of functions and sets.

What real-world applications do the Hairy Ball and Fixed Point Theorems have?

The Hairy Ball and Fixed Point Theorems have many applications in fields such as physics, computer science, and economics. In physics, the Hairy Ball Theorem is used to explain the existence of vortexes in fluid dynamics. In computer science, the Fixed Point Theorem is used in algorithms for finding solutions to optimization problems. In economics, the Fixed Point Theorem is used to prove the existence of equilibrium points in market models.

Are there any exceptions to the Hairy Ball and Fixed Point Theorems?

Yes, there are exceptions to both the Hairy Ball and Fixed Point Theorems. For the Hairy Ball Theorem, there are exceptions when the dimension of the ball is odd, as well as for certain non-continuous functions. For the Fixed Point Theorem, there are exceptions when the set is not compact or convex. However, these exceptions are rare and do not diminish the overall significance of these theorems.

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