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They are sets with a finite number of elements. For example the days of the week, or the 12 months of the year. Modular arithmetic is based on finite sets.
Closed sets and open sets, or finite and infinite sets.
sets
Closed sets and open sets, or finite and infinite sets.
A countable set is defined as one whose elements can be put into one-to-one correspondence with elements of the set of counting numbers or some subset of it. A countable set can be infinite: for example all even numbers. This raises the strange concept where a subset (positive even numbers) has the same cardinality as all counting numbers - which should be a set that is twice as large! Even more confusingly (perhaps) is the fact that the set of all rational numbers also has the same cardinality as the set of counting numbers. You need to go to the set of irrationals or bigger before you get to uncountable sets. So you have the weird situation in which there are more irrationals between 0 and 1 than there are rationals between from 0 and infinity (if infinity can be treated as a value)! There is a minority definition of countable which means containing a finite number of elements as opposed to uncountable meaning infinitely many elements. However, these definitions are essentially the same as the finite sets and infinite sets and so there is little point in using them.
YES
here is the proof: http://planetmath.org/encyclopedia/ProductOfAFiniteNumberOfCountableSetsIsCountable.html
It is a measure, but it isn't always sigma-finite. Take your space X = [0,1], and u = counting measure if u(E) < infinity, then E is a finite set, but there is no way to cover the uncountable set [0,1] by a countable collection of finite sets.
They are sets with a finite number of elements. For example the days of the week, or the 12 months of the year. Modular arithmetic is based on finite sets.
Closed sets and open sets, or finite and infinite sets.
sets
Closed sets and open sets, or finite and infinite sets.
Closed sets and open sets, or finite and infinite sets.
Closed sets and open sets, or finite and infinite sets.
CHECK THIS OUT http://www.mathstat.dal.ca/~hill/2112/assn7sol.pdf
A countable set is defined as one whose elements can be put into one-to-one correspondence with elements of the set of counting numbers or some subset of it. A countable set can be infinite: for example all even numbers. This raises the strange concept where a subset (positive even numbers) has the same cardinality as all counting numbers - which should be a set that is twice as large! Even more confusingly (perhaps) is the fact that the set of all rational numbers also has the same cardinality as the set of counting numbers. You need to go to the set of irrationals or bigger before you get to uncountable sets. So you have the weird situation in which there are more irrationals between 0 and 1 than there are rationals between from 0 and infinity (if infinity can be treated as a value)! There is a minority definition of countable which means containing a finite number of elements as opposed to uncountable meaning infinitely many elements. However, these definitions are essentially the same as the finite sets and infinite sets and so there is little point in using them.
They are numbers that terminate.