Examples of using Choice function in English and their translations into Greek
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Every set has a choice function.[5].
Easy choice functions and programs.
Travel speed normal/cutback choice function.
Design EQ sound choice function, achieve high quality music effect.
For any set A, the powerset of A(minus the empty set)has a choice function.
No social choice function meets these requirements in an ordinal scale simultaneously.
For any set A, the power set of A(with the empty set removed)has a choice function.
Then our choice function can choose the least element of every set under our unusual ordering.".
Axiom- For any set X of nonempty sets,there exists a choice function f defined on X.
With this alternate notion of choice function, the axiom of choice can be compactly stated as.
Thus the negation of the axiom of choice states that there exists a set of nonempty sets which has no choice function.
Each choice function on a collection X of nonempty sets is an element of the Cartesian product of the sets in X.
Other colorings, this game is notable for its fnogofunktsionalnostyu,in particular there is a choice function gradient coloring.
One variation avoids the use of choice functions by, in effect,replacing each choice function with its range.
Another equivalent axiom only considers collections X that are essentially powersets of other sets: For any set A, the power set of A(with the empty set removed)has a choice function.
Every such subset has a smallest element,so to specify our choice function we can simply say that it maps each set to the least element of that set.
A choice function is a function f, defined on a collection X of nonempty sets, such that for every set A in X, f(A) is an element of A. With this concept, the axiom can be stated.
A still weaker example is the axiom of countable choice(ACω or CC),which states that a choice function exists for any countable set of nonempty sets.
The result is an explicit choice function: a function that takes the first box to the first element we chose, the second box to the second element we chose, and so on.
Every nonempty set of natural numbers has a smallest element,so to specify our choice function we can simply say that it takes each set to the least element of that set.
(A formal proof for all finite sets would use the principle of mathematical induction to prove"for every natural number k,every family of k nonempty sets has a choice function.").
Authors who use this formulation often speak of the choice function on A, but be advised that this is a slightly different notion of choice function.
The statement of the axiom of choice does not specify whether the collection of nonempty sets is finite or infinite, andthus implies that every finite collection of nonempty sets has a choice function.
This method cannot, however,be used to show that every countable family of nonempty sets has a choice function, as is asserted by the axiom of countable choice. .
In the even simpler case of a collection of"one" set, a choice function just corresponds to an element, so this instance of the axiom of choice says that every nonempty set has an element; this holds trivially.
If we try to choose an element from each set, then, because X is infinite, our choice procedure will never come to an end, and consequently,we shall never be able to produce a choice function for all of X.
If the method is applied to an infinite sequence(Xi: i∈ω) of nonempty sets,a function is obtained at each finite stage, but there is no stage at which a choice function for the entire family is constructed, and no"limiting" choice function can be constructed, in general, in ZF without the axiom of choice. .
If we try to choose an element from each set, then, because X is infinite, our choice procedure will never come to an end, and consequently,we will never be able to produce a choice function for all of X. So that won't work.
If we try to choose an element from each set, then, because X is infinite, our choice procedure will never come to an end, and consequently,we will never be able to produce a choice function for all of X. Next we might try specifying the least element from each set.
For example, if we abbreviate by BP the claim that every set of real numbers has the property of Baire, then BP is stronger than¬AC,which asserts the nonexistence of any choice function on perhaps only a single set of nonempty sets.