$f$ integrable on $A times B$, show subset of $A$ is negligible












3












$begingroup$


$A subset mathbb R^m$ and $B subset mathbb R^n$ are boxes, and $f$ is integrable in the riemann sense on $(Atimes B)$.



We define $$A_1 =left{a in A left|exists int_{B}f(a,b)dbright.right} subset A.$$



Show that $A setminus A_1$ has zero volume.










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$endgroup$












  • $begingroup$
    I have a strong feeling this is related to Fubini's theorem. Something along the lines of $int_{A times B} f = int_{A} int_B f(a,b)dbda = int_{A_1}int_B f(a,b)dbda + int_{A setminus A_1}int_B f(a,b)dbda$
    $endgroup$
    – Oria Gruber
    Dec 23 '18 at 20:50


















3












$begingroup$


$A subset mathbb R^m$ and $B subset mathbb R^n$ are boxes, and $f$ is integrable in the riemann sense on $(Atimes B)$.



We define $$A_1 =left{a in A left|exists int_{B}f(a,b)dbright.right} subset A.$$



Show that $A setminus A_1$ has zero volume.










share|cite|improve this question











$endgroup$












  • $begingroup$
    I have a strong feeling this is related to Fubini's theorem. Something along the lines of $int_{A times B} f = int_{A} int_B f(a,b)dbda = int_{A_1}int_B f(a,b)dbda + int_{A setminus A_1}int_B f(a,b)dbda$
    $endgroup$
    – Oria Gruber
    Dec 23 '18 at 20:50
















3












3








3





$begingroup$


$A subset mathbb R^m$ and $B subset mathbb R^n$ are boxes, and $f$ is integrable in the riemann sense on $(Atimes B)$.



We define $$A_1 =left{a in A left|exists int_{B}f(a,b)dbright.right} subset A.$$



Show that $A setminus A_1$ has zero volume.










share|cite|improve this question











$endgroup$




$A subset mathbb R^m$ and $B subset mathbb R^n$ are boxes, and $f$ is integrable in the riemann sense on $(Atimes B)$.



We define $$A_1 =left{a in A left|exists int_{B}f(a,b)dbright.right} subset A.$$



Show that $A setminus A_1$ has zero volume.







integration measure-theory






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 23 '18 at 20:37









gt6989b

36k22557




36k22557










asked Dec 23 '18 at 20:18









Oria GruberOria Gruber

6,54232464




6,54232464












  • $begingroup$
    I have a strong feeling this is related to Fubini's theorem. Something along the lines of $int_{A times B} f = int_{A} int_B f(a,b)dbda = int_{A_1}int_B f(a,b)dbda + int_{A setminus A_1}int_B f(a,b)dbda$
    $endgroup$
    – Oria Gruber
    Dec 23 '18 at 20:50




















  • $begingroup$
    I have a strong feeling this is related to Fubini's theorem. Something along the lines of $int_{A times B} f = int_{A} int_B f(a,b)dbda = int_{A_1}int_B f(a,b)dbda + int_{A setminus A_1}int_B f(a,b)dbda$
    $endgroup$
    – Oria Gruber
    Dec 23 '18 at 20:50


















$begingroup$
I have a strong feeling this is related to Fubini's theorem. Something along the lines of $int_{A times B} f = int_{A} int_B f(a,b)dbda = int_{A_1}int_B f(a,b)dbda + int_{A setminus A_1}int_B f(a,b)dbda$
$endgroup$
– Oria Gruber
Dec 23 '18 at 20:50






$begingroup$
I have a strong feeling this is related to Fubini's theorem. Something along the lines of $int_{A times B} f = int_{A} int_B f(a,b)dbda = int_{A_1}int_B f(a,b)dbda + int_{A setminus A_1}int_B f(a,b)dbda$
$endgroup$
– Oria Gruber
Dec 23 '18 at 20:50












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