Need help solving proof involving equivalence relation












0












$begingroup$


Prop: Let ~ be an equivalence relation on a set A, and a, b ∈ A. If a ~ b, then [a] = [b] and if a ≁ b, then [a] ∩ [b] = ∅.



What I understand so far: an equivalence relation has to have 3 properties: reflexive, symmetric, and transitivity. Both a and b are elements of the set A and the questions asking if a and b's cardinality are equal and if a is not an equivalence relation to b, then the intersection of there cardinality must be equal to the empty set.



However I don't quite understand how to write a proof for this proposition, an elementary proof would be absolutely amazing alongside some explanation.



Thank you for all the support math.StackExchange members!






discrete-mathematics







share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    It's not asking about cardinality.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:15










  • $begingroup$
    that would explain my confusion as the cardinality of an element makes absolutely no sense. I don't quite understand what the question is asking..
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:16








  • 1




    $begingroup$
    $[a]$ is the equivalence class of $a$ under the relation.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:17










  • $begingroup$
    $[a]={ x in A | x sim a }$ ... does that help?
    $endgroup$
    – Bram28
    Dec 16 '18 at 2:33










  • $begingroup$
    Not really, sorry.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 3:00
















0












$begingroup$


Prop: Let ~ be an equivalence relation on a set A, and a, b ∈ A. If a ~ b, then [a] = [b] and if a ≁ b, then [a] ∩ [b] = ∅.



What I understand so far: an equivalence relation has to have 3 properties: reflexive, symmetric, and transitivity. Both a and b are elements of the set A and the questions asking if a and b's cardinality are equal and if a is not an equivalence relation to b, then the intersection of there cardinality must be equal to the empty set.



However I don't quite understand how to write a proof for this proposition, an elementary proof would be absolutely amazing alongside some explanation.



Thank you for all the support math.StackExchange members!






discrete-mathematics







share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    It's not asking about cardinality.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:15










  • $begingroup$
    that would explain my confusion as the cardinality of an element makes absolutely no sense. I don't quite understand what the question is asking..
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:16








  • 1




    $begingroup$
    $[a]$ is the equivalence class of $a$ under the relation.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:17










  • $begingroup$
    $[a]={ x in A | x sim a }$ ... does that help?
    $endgroup$
    – Bram28
    Dec 16 '18 at 2:33










  • $begingroup$
    Not really, sorry.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 3:00














0












0








0





$begingroup$


Prop: Let ~ be an equivalence relation on a set A, and a, b ∈ A. If a ~ b, then [a] = [b] and if a ≁ b, then [a] ∩ [b] = ∅.



What I understand so far: an equivalence relation has to have 3 properties: reflexive, symmetric, and transitivity. Both a and b are elements of the set A and the questions asking if a and b's cardinality are equal and if a is not an equivalence relation to b, then the intersection of there cardinality must be equal to the empty set.



However I don't quite understand how to write a proof for this proposition, an elementary proof would be absolutely amazing alongside some explanation.



Thank you for all the support math.StackExchange members!






discrete-mathematics







share|cite|improve this question









$endgroup$




Prop: Let ~ be an equivalence relation on a set A, and a, b ∈ A. If a ~ b, then [a] = [b] and if a ≁ b, then [a] ∩ [b] = ∅.



What I understand so far: an equivalence relation has to have 3 properties: reflexive, symmetric, and transitivity. Both a and b are elements of the set A and the questions asking if a and b's cardinality are equal and if a is not an equivalence relation to b, then the intersection of there cardinality must be equal to the empty set.



However I don't quite understand how to write a proof for this proposition, an elementary proof would be absolutely amazing alongside some explanation.



Thank you for all the support math.StackExchange members!






discrete-mathematics




discrete-mathematics






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Dec 16 '18 at 2:14









Zdravstvuyte94Zdravstvuyte94

465




465








  • 1




    $begingroup$
    It's not asking about cardinality.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:15










  • $begingroup$
    that would explain my confusion as the cardinality of an element makes absolutely no sense. I don't quite understand what the question is asking..
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:16








  • 1




    $begingroup$
    $[a]$ is the equivalence class of $a$ under the relation.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:17










  • $begingroup$
    $[a]={ x in A | x sim a }$ ... does that help?
    $endgroup$
    – Bram28
    Dec 16 '18 at 2:33










  • $begingroup$
    Not really, sorry.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 3:00














  • 1




    $begingroup$
    It's not asking about cardinality.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:15










  • $begingroup$
    that would explain my confusion as the cardinality of an element makes absolutely no sense. I don't quite understand what the question is asking..
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:16








  • 1




    $begingroup$
    $[a]$ is the equivalence class of $a$ under the relation.
    $endgroup$
    – Randall
    Dec 16 '18 at 2:17










  • $begingroup$
    $[a]={ x in A | x sim a }$ ... does that help?
    $endgroup$
    – Bram28
    Dec 16 '18 at 2:33










  • $begingroup$
    Not really, sorry.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 3:00








1




1




$begingroup$
It's not asking about cardinality.
$endgroup$
– Randall
Dec 16 '18 at 2:15




$begingroup$
It's not asking about cardinality.
$endgroup$
– Randall
Dec 16 '18 at 2:15












$begingroup$
that would explain my confusion as the cardinality of an element makes absolutely no sense. I don't quite understand what the question is asking..
$endgroup$
– Zdravstvuyte94
Dec 16 '18 at 2:16






$begingroup$
that would explain my confusion as the cardinality of an element makes absolutely no sense. I don't quite understand what the question is asking..
$endgroup$
– Zdravstvuyte94
Dec 16 '18 at 2:16






1




1




$begingroup$
$[a]$ is the equivalence class of $a$ under the relation.
$endgroup$
– Randall
Dec 16 '18 at 2:17




$begingroup$
$[a]$ is the equivalence class of $a$ under the relation.
$endgroup$
– Randall
Dec 16 '18 at 2:17












$begingroup$
$[a]={ x in A | x sim a }$ ... does that help?
$endgroup$
– Bram28
Dec 16 '18 at 2:33




$begingroup$
$[a]={ x in A | x sim a }$ ... does that help?
$endgroup$
– Bram28
Dec 16 '18 at 2:33












$begingroup$
Not really, sorry.
$endgroup$
– Zdravstvuyte94
Dec 16 '18 at 3:00




$begingroup$
Not really, sorry.
$endgroup$
– Zdravstvuyte94
Dec 16 '18 at 3:00










1 Answer
1






active

oldest

votes


















1












$begingroup$

Suppose $[a]cap[b] neq emptyset$. Then there is a $c in [a]cap[b]$. Then, by the definition of equivalence classes and intersection, $asim c land csim b$. By the transitivity of equivalence relations, $asim b$: contradiction.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    I don't understand that proof, I guess equivalence classes are confusing me a bit here.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:59










  • $begingroup$
    Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
    $endgroup$
    – Ross Millikan
    Dec 16 '18 at 3:01











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$begingroup$

Suppose $[a]cap[b] neq emptyset$. Then there is a $c in [a]cap[b]$. Then, by the definition of equivalence classes and intersection, $asim c land csim b$. By the transitivity of equivalence relations, $asim b$: contradiction.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    I don't understand that proof, I guess equivalence classes are confusing me a bit here.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:59










  • $begingroup$
    Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
    $endgroup$
    – Ross Millikan
    Dec 16 '18 at 3:01
















1












$begingroup$

Suppose $[a]cap[b] neq emptyset$. Then there is a $c in [a]cap[b]$. Then, by the definition of equivalence classes and intersection, $asim c land csim b$. By the transitivity of equivalence relations, $asim b$: contradiction.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    I don't understand that proof, I guess equivalence classes are confusing me a bit here.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:59










  • $begingroup$
    Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
    $endgroup$
    – Ross Millikan
    Dec 16 '18 at 3:01














1












1








1





$begingroup$

Suppose $[a]cap[b] neq emptyset$. Then there is a $c in [a]cap[b]$. Then, by the definition of equivalence classes and intersection, $asim c land csim b$. By the transitivity of equivalence relations, $asim b$: contradiction.






share|cite|improve this answer











$endgroup$



Suppose $[a]cap[b] neq emptyset$. Then there is a $c in [a]cap[b]$. Then, by the definition of equivalence classes and intersection, $asim c land csim b$. By the transitivity of equivalence relations, $asim b$: contradiction.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Dec 17 '18 at 0:04

























answered Dec 16 '18 at 2:30









Lucas HenriqueLucas Henrique

1,036414




1,036414












  • $begingroup$
    I don't understand that proof, I guess equivalence classes are confusing me a bit here.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:59










  • $begingroup$
    Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
    $endgroup$
    – Ross Millikan
    Dec 16 '18 at 3:01


















  • $begingroup$
    I don't understand that proof, I guess equivalence classes are confusing me a bit here.
    $endgroup$
    – Zdravstvuyte94
    Dec 16 '18 at 2:59










  • $begingroup$
    Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
    $endgroup$
    – Ross Millikan
    Dec 16 '18 at 3:01
















$begingroup$
I don't understand that proof, I guess equivalence classes are confusing me a bit here.
$endgroup$
– Zdravstvuyte94
Dec 16 '18 at 2:59




$begingroup$
I don't understand that proof, I guess equivalence classes are confusing me a bit here.
$endgroup$
– Zdravstvuyte94
Dec 16 '18 at 2:59












$begingroup$
Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
$endgroup$
– Ross Millikan
Dec 16 '18 at 3:01




$begingroup$
Then you need to study the definitions of each of reflexive, symmetric, and transitive as properties of relations. When you have an equivalence relation the set is divided into equivalence classes. All the elements in a class are related and no elements that are in different classes are related.
$endgroup$
– Ross Millikan
Dec 16 '18 at 3:01


















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