Proof verification- $ sigma $ - Algebra, Algebra, Ring












2












$begingroup$


I want to prove following for a set $ X neq emptyset $ :
$ M subset P(X) $, where $ P(X) $ is the power set.



1) Any Ring is an Algebra



2) Any Algebra is a Ring



3) Any Ring is a $ sigma $ -Algebra



4) Any Algebra is a $ sigma $- Algebra



5) Any $ sigma $- Algebra is an Algebra



For a set $ X neq emptyset $, $M$ is



a) A Ring if




  • $ emptyset in M$


  • $ A,B in M rightarrow A cup B in M $


  • $ A,B in M rightarrow B backslash A in M $



b) An Algebra, if $ M$ Ring , and $ X in M $



c) A $ sigma $-Algebra if




  • $ X in M $


  • $ A in M rightarrow X backslash A in M $


  • $ (A_i)_{i in mathbb{N}} in M rightarrow cup_{i=0}^{ infty} A_i in M $





for 1)
For $ A subset X $ is M:={ emptyset , A} a Ring, but for $ A neq X$ not an Algebra.



2)
let be $ A,B in M $



$ A backslash B = ( A^c cup B )^c in M $
So M is also a ring.



3)
I guess I can use the same example as for 1)?



4) let be $ X= mathbb{N} , M:= { A subset X : A $ or $ A^c $ finite $}$
is this a right example for an Alegbra , which is not a s.Algeba?



5)
$A,B in M $



$ X= X backslash emptyset in M $



$ Abackslash B = A cap B^c = ( A^c cup B)^c in M $



any union you can discribe as :
$ A cup B = A cup B cup emptyset cup ...emptyset in M $



so any s. Algebra is also an Algebra.



are my arguments correct and formally right? any adjustments?
Appreciate any of your help !










share|cite|improve this question











$endgroup$












  • $begingroup$
    What is the role of the set $;X;$ in all those question ...??
    $endgroup$
    – DonAntonio
    Jan 23 at 13:58










  • $begingroup$
    it's a random set..if that's what you mean.?
    $endgroup$
    – wondering1123
    Jan 23 at 16:47










  • $begingroup$
    Do you see how to go from boolean algebra on $M $ to $sigma$-algebra on $M$ ? $A . B = A cap B$ and $A + B =...$
    $endgroup$
    – reuns
    Jan 23 at 22:03


















2












$begingroup$


I want to prove following for a set $ X neq emptyset $ :
$ M subset P(X) $, where $ P(X) $ is the power set.



1) Any Ring is an Algebra



2) Any Algebra is a Ring



3) Any Ring is a $ sigma $ -Algebra



4) Any Algebra is a $ sigma $- Algebra



5) Any $ sigma $- Algebra is an Algebra



For a set $ X neq emptyset $, $M$ is



a) A Ring if




  • $ emptyset in M$


  • $ A,B in M rightarrow A cup B in M $


  • $ A,B in M rightarrow B backslash A in M $



b) An Algebra, if $ M$ Ring , and $ X in M $



c) A $ sigma $-Algebra if




  • $ X in M $


  • $ A in M rightarrow X backslash A in M $


  • $ (A_i)_{i in mathbb{N}} in M rightarrow cup_{i=0}^{ infty} A_i in M $





for 1)
For $ A subset X $ is M:={ emptyset , A} a Ring, but for $ A neq X$ not an Algebra.



2)
let be $ A,B in M $



$ A backslash B = ( A^c cup B )^c in M $
So M is also a ring.



3)
I guess I can use the same example as for 1)?



4) let be $ X= mathbb{N} , M:= { A subset X : A $ or $ A^c $ finite $}$
is this a right example for an Alegbra , which is not a s.Algeba?



5)
$A,B in M $



$ X= X backslash emptyset in M $



$ Abackslash B = A cap B^c = ( A^c cup B)^c in M $



any union you can discribe as :
$ A cup B = A cup B cup emptyset cup ...emptyset in M $



so any s. Algebra is also an Algebra.



are my arguments correct and formally right? any adjustments?
Appreciate any of your help !










share|cite|improve this question











$endgroup$












  • $begingroup$
    What is the role of the set $;X;$ in all those question ...??
    $endgroup$
    – DonAntonio
    Jan 23 at 13:58










  • $begingroup$
    it's a random set..if that's what you mean.?
    $endgroup$
    – wondering1123
    Jan 23 at 16:47










  • $begingroup$
    Do you see how to go from boolean algebra on $M $ to $sigma$-algebra on $M$ ? $A . B = A cap B$ and $A + B =...$
    $endgroup$
    – reuns
    Jan 23 at 22:03
















2












2








2





$begingroup$


I want to prove following for a set $ X neq emptyset $ :
$ M subset P(X) $, where $ P(X) $ is the power set.



1) Any Ring is an Algebra



2) Any Algebra is a Ring



3) Any Ring is a $ sigma $ -Algebra



4) Any Algebra is a $ sigma $- Algebra



5) Any $ sigma $- Algebra is an Algebra



For a set $ X neq emptyset $, $M$ is



a) A Ring if




  • $ emptyset in M$


  • $ A,B in M rightarrow A cup B in M $


  • $ A,B in M rightarrow B backslash A in M $



b) An Algebra, if $ M$ Ring , and $ X in M $



c) A $ sigma $-Algebra if




  • $ X in M $


  • $ A in M rightarrow X backslash A in M $


  • $ (A_i)_{i in mathbb{N}} in M rightarrow cup_{i=0}^{ infty} A_i in M $





for 1)
For $ A subset X $ is M:={ emptyset , A} a Ring, but for $ A neq X$ not an Algebra.



2)
let be $ A,B in M $



$ A backslash B = ( A^c cup B )^c in M $
So M is also a ring.



3)
I guess I can use the same example as for 1)?



4) let be $ X= mathbb{N} , M:= { A subset X : A $ or $ A^c $ finite $}$
is this a right example for an Alegbra , which is not a s.Algeba?



5)
$A,B in M $



$ X= X backslash emptyset in M $



$ Abackslash B = A cap B^c = ( A^c cup B)^c in M $



any union you can discribe as :
$ A cup B = A cup B cup emptyset cup ...emptyset in M $



so any s. Algebra is also an Algebra.



are my arguments correct and formally right? any adjustments?
Appreciate any of your help !










share|cite|improve this question











$endgroup$




I want to prove following for a set $ X neq emptyset $ :
$ M subset P(X) $, where $ P(X) $ is the power set.



1) Any Ring is an Algebra



2) Any Algebra is a Ring



3) Any Ring is a $ sigma $ -Algebra



4) Any Algebra is a $ sigma $- Algebra



5) Any $ sigma $- Algebra is an Algebra



For a set $ X neq emptyset $, $M$ is



a) A Ring if




  • $ emptyset in M$


  • $ A,B in M rightarrow A cup B in M $


  • $ A,B in M rightarrow B backslash A in M $



b) An Algebra, if $ M$ Ring , and $ X in M $



c) A $ sigma $-Algebra if




  • $ X in M $


  • $ A in M rightarrow X backslash A in M $


  • $ (A_i)_{i in mathbb{N}} in M rightarrow cup_{i=0}^{ infty} A_i in M $





for 1)
For $ A subset X $ is M:={ emptyset , A} a Ring, but for $ A neq X$ not an Algebra.



2)
let be $ A,B in M $



$ A backslash B = ( A^c cup B )^c in M $
So M is also a ring.



3)
I guess I can use the same example as for 1)?



4) let be $ X= mathbb{N} , M:= { A subset X : A $ or $ A^c $ finite $}$
is this a right example for an Alegbra , which is not a s.Algeba?



5)
$A,B in M $



$ X= X backslash emptyset in M $



$ Abackslash B = A cap B^c = ( A^c cup B)^c in M $



any union you can discribe as :
$ A cup B = A cup B cup emptyset cup ...emptyset in M $



so any s. Algebra is also an Algebra.



are my arguments correct and formally right? any adjustments?
Appreciate any of your help !







real-analysis measure-theory proof-verification elementary-set-theory






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 23 at 22:49









Andrés E. Caicedo

65.7k8160250




65.7k8160250










asked Jan 23 at 13:51









wondering1123wondering1123

14911




14911












  • $begingroup$
    What is the role of the set $;X;$ in all those question ...??
    $endgroup$
    – DonAntonio
    Jan 23 at 13:58










  • $begingroup$
    it's a random set..if that's what you mean.?
    $endgroup$
    – wondering1123
    Jan 23 at 16:47










  • $begingroup$
    Do you see how to go from boolean algebra on $M $ to $sigma$-algebra on $M$ ? $A . B = A cap B$ and $A + B =...$
    $endgroup$
    – reuns
    Jan 23 at 22:03




















  • $begingroup$
    What is the role of the set $;X;$ in all those question ...??
    $endgroup$
    – DonAntonio
    Jan 23 at 13:58










  • $begingroup$
    it's a random set..if that's what you mean.?
    $endgroup$
    – wondering1123
    Jan 23 at 16:47










  • $begingroup$
    Do you see how to go from boolean algebra on $M $ to $sigma$-algebra on $M$ ? $A . B = A cap B$ and $A + B =...$
    $endgroup$
    – reuns
    Jan 23 at 22:03


















$begingroup$
What is the role of the set $;X;$ in all those question ...??
$endgroup$
– DonAntonio
Jan 23 at 13:58




$begingroup$
What is the role of the set $;X;$ in all those question ...??
$endgroup$
– DonAntonio
Jan 23 at 13:58












$begingroup$
it's a random set..if that's what you mean.?
$endgroup$
– wondering1123
Jan 23 at 16:47




$begingroup$
it's a random set..if that's what you mean.?
$endgroup$
– wondering1123
Jan 23 at 16:47












$begingroup$
Do you see how to go from boolean algebra on $M $ to $sigma$-algebra on $M$ ? $A . B = A cap B$ and $A + B =...$
$endgroup$
– reuns
Jan 23 at 22:03






$begingroup$
Do you see how to go from boolean algebra on $M $ to $sigma$-algebra on $M$ ? $A . B = A cap B$ and $A + B =...$
$endgroup$
– reuns
Jan 23 at 22:03












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