Are the elements of this set distinct? Can it be considered a set if they are not?
$begingroup$
I'm currently reading Book of Proof by Richard Hammack. In the chapter on sets, he gives this as an example:
X = { n2 : n ∈ Z }
If n can be any integer and (-n)2 = (n)2, are the elements of this set distinct? If they are not, is this a set?
To my understanding, sets cannot have repeated elements. However, on the wikipedia page for sets it defines a set as
a collection of distinct objects, considered as an object in its own right
but later says
In an extensional definition, a set member can be listed two or more times, for example, {11, 6, 6}.
So can sets have repeated elements?
elementary-set-theory
$endgroup$
add a comment |
$begingroup$
I'm currently reading Book of Proof by Richard Hammack. In the chapter on sets, he gives this as an example:
X = { n2 : n ∈ Z }
If n can be any integer and (-n)2 = (n)2, are the elements of this set distinct? If they are not, is this a set?
To my understanding, sets cannot have repeated elements. However, on the wikipedia page for sets it defines a set as
a collection of distinct objects, considered as an object in its own right
but later says
In an extensional definition, a set member can be listed two or more times, for example, {11, 6, 6}.
So can sets have repeated elements?
elementary-set-theory
$endgroup$
add a comment |
$begingroup$
I'm currently reading Book of Proof by Richard Hammack. In the chapter on sets, he gives this as an example:
X = { n2 : n ∈ Z }
If n can be any integer and (-n)2 = (n)2, are the elements of this set distinct? If they are not, is this a set?
To my understanding, sets cannot have repeated elements. However, on the wikipedia page for sets it defines a set as
a collection of distinct objects, considered as an object in its own right
but later says
In an extensional definition, a set member can be listed two or more times, for example, {11, 6, 6}.
So can sets have repeated elements?
elementary-set-theory
$endgroup$
I'm currently reading Book of Proof by Richard Hammack. In the chapter on sets, he gives this as an example:
X = { n2 : n ∈ Z }
If n can be any integer and (-n)2 = (n)2, are the elements of this set distinct? If they are not, is this a set?
To my understanding, sets cannot have repeated elements. However, on the wikipedia page for sets it defines a set as
a collection of distinct objects, considered as an object in its own right
but later says
In an extensional definition, a set member can be listed two or more times, for example, {11, 6, 6}.
So can sets have repeated elements?
elementary-set-theory
elementary-set-theory
asked Dec 4 '18 at 14:16
Copeland CorleyCopeland Corley
82
82
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
Think of it like this: an element $x$ of a set $A$ can be mentioned in the notation of the set more than once.
Here ${11,6,6}$ is a notation of the unique set that only has the elements $6$ and $11$ (and is completely determined by that fact) and in this notation element $6$ is mentioned twice. That is allowed.
That's all.
$endgroup$
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
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Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
add a comment |
$begingroup$
Yes, it is a set. Note that ${1,1}$ and ${1}$ are the same set. So$$X={1,1,4,4,9,9,16,16,ldots}={1,4,9,16,ldots}$$
$endgroup$
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
add a comment |
$begingroup$
The notation allows to repeat the elements, but as they are identical, they "count once" only. So, strictly,
$${11,6,6}={11,6}.$$
True replication requires a multiset.
$endgroup$
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
add a comment |
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3 Answers
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3 Answers
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$begingroup$
Think of it like this: an element $x$ of a set $A$ can be mentioned in the notation of the set more than once.
Here ${11,6,6}$ is a notation of the unique set that only has the elements $6$ and $11$ (and is completely determined by that fact) and in this notation element $6$ is mentioned twice. That is allowed.
That's all.
$endgroup$
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
$begingroup$
Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
add a comment |
$begingroup$
Think of it like this: an element $x$ of a set $A$ can be mentioned in the notation of the set more than once.
Here ${11,6,6}$ is a notation of the unique set that only has the elements $6$ and $11$ (and is completely determined by that fact) and in this notation element $6$ is mentioned twice. That is allowed.
That's all.
$endgroup$
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
$begingroup$
Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
add a comment |
$begingroup$
Think of it like this: an element $x$ of a set $A$ can be mentioned in the notation of the set more than once.
Here ${11,6,6}$ is a notation of the unique set that only has the elements $6$ and $11$ (and is completely determined by that fact) and in this notation element $6$ is mentioned twice. That is allowed.
That's all.
$endgroup$
Think of it like this: an element $x$ of a set $A$ can be mentioned in the notation of the set more than once.
Here ${11,6,6}$ is a notation of the unique set that only has the elements $6$ and $11$ (and is completely determined by that fact) and in this notation element $6$ is mentioned twice. That is allowed.
That's all.
answered Dec 4 '18 at 14:27
drhabdrhab
102k545136
102k545136
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
$begingroup$
Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
add a comment |
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
$begingroup$
Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
So how would I distinguish a set that mentions an element multiple times and a multiset that contains multiple identical objects that are separate elementst?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:36
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
By paying attention to the context that you are working in, I would say. Multisets and sets are distinct mathematical objects. Also see here where is mentioned e.g."...to distinguish between sets and multisets, a notation that incorporates square brackets is sometimes used: the multiset ${a,a,b}$ can be denoted as $[a, a, b]$...". I assure you that if you once work with multisets then you will certainly be aware of that too :-). In your question you only mention sets and not multisets.
$endgroup$
– drhab
Dec 4 '18 at 14:58
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
$begingroup$
One final question. Since {11, 6} and {11, 6, 6} are the same set, do they have the same cardinality?
$endgroup$
– Copeland Corley
Dec 4 '18 at 15:33
$begingroup$
Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
$begingroup$
Yes, they do. The cardinality is $2$ as you will understand.
$endgroup$
– drhab
Dec 4 '18 at 16:40
add a comment |
$begingroup$
Yes, it is a set. Note that ${1,1}$ and ${1}$ are the same set. So$$X={1,1,4,4,9,9,16,16,ldots}={1,4,9,16,ldots}$$
$endgroup$
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
add a comment |
$begingroup$
Yes, it is a set. Note that ${1,1}$ and ${1}$ are the same set. So$$X={1,1,4,4,9,9,16,16,ldots}={1,4,9,16,ldots}$$
$endgroup$
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
add a comment |
$begingroup$
Yes, it is a set. Note that ${1,1}$ and ${1}$ are the same set. So$$X={1,1,4,4,9,9,16,16,ldots}={1,4,9,16,ldots}$$
$endgroup$
Yes, it is a set. Note that ${1,1}$ and ${1}$ are the same set. So$$X={1,1,4,4,9,9,16,16,ldots}={1,4,9,16,ldots}$$
answered Dec 4 '18 at 14:19
José Carlos SantosJosé Carlos Santos
164k22131234
164k22131234
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
add a comment |
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
Okay, so if I have the set {1,1} and the multiset {1,1}, they are not equal, right?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:39
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
$begingroup$
I have no experience whatsoever with multisets.
$endgroup$
– José Carlos Santos
Dec 4 '18 at 14:40
add a comment |
$begingroup$
The notation allows to repeat the elements, but as they are identical, they "count once" only. So, strictly,
$${11,6,6}={11,6}.$$
True replication requires a multiset.
$endgroup$
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
add a comment |
$begingroup$
The notation allows to repeat the elements, but as they are identical, they "count once" only. So, strictly,
$${11,6,6}={11,6}.$$
True replication requires a multiset.
$endgroup$
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
add a comment |
$begingroup$
The notation allows to repeat the elements, but as they are identical, they "count once" only. So, strictly,
$${11,6,6}={11,6}.$$
True replication requires a multiset.
$endgroup$
The notation allows to repeat the elements, but as they are identical, they "count once" only. So, strictly,
$${11,6,6}={11,6}.$$
True replication requires a multiset.
answered Dec 4 '18 at 14:28
Yves DaoustYves Daoust
129k675227
129k675227
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
add a comment |
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
How would I know that I am dealing with a set instead of a multiset? Is it supposed to be inferred from the context?
$endgroup$
– Copeland Corley
Dec 4 '18 at 14:37
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
$begingroup$
@CopelandCorley: of course. Multisets aren't so often met.
$endgroup$
– Yves Daoust
Dec 4 '18 at 14:55
add a comment |
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