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## Main Question or Discussion Point

Suppose that A is subset of R (real line) with the property for every ε > 0 there are measurable sets B and C s.t. B⊂A⊂C and m(C\B)<ε

Prove A is measurable

By definition A is measurable we need to prove m(E)=m(E∩A)+m(E\A) for all E

the ≤ is trivial enough to show ≥:

Since C is measurable then m(E)= m(E∩C)+m(E\C)

≥ m(E∩A)+m(E\A)-ε (Since A is subset of C)

then move the ε to LHS and since for every ε so, let ε->0 , obtain the result.

is my solution right??? i thought i should use B and m(C\B)<ε somewhere. Could some one help me to check it??

many thanks

Prove A is measurable

By definition A is measurable we need to prove m(E)=m(E∩A)+m(E\A) for all E

the ≤ is trivial enough to show ≥:

Since C is measurable then m(E)= m(E∩C)+m(E\C)

≥ m(E∩A)+m(E\A)-ε (Since A is subset of C)

then move the ε to LHS and since for every ε so, let ε->0 , obtain the result.

is my solution right??? i thought i should use B and m(C\B)<ε somewhere. Could some one help me to check it??

many thanks