# Zero content

• Nov 17th 2009, 08:47 PM
amoeba
Zero content
A set z in R is said to have zero content if for any epsilon > 0, there is a finite collection of intervals I1, ...IL such that z is a subset of the union of those intervals (meaning all points in z are contained in the union of all the intervals) AND the sum of the lengths of the intervals is less than epsilon.

Thus, I was wondering if I could clarify something about zero content. So, for example, the set z = {y : y = x^2, x is part of [0, 10]} would not have zero content because for all the points z to be contained in intervals, the length of union of the intervals must be 10 and epsilon can be found which is less than 10.

However, am I right in thinking that the set z = {y : y = x^2, x is part of integers} has zero content? This is because arbitarily small intervals can be chosen around those points, and the union of the intervals can be made less than epsilon.

So basically, if f is continuous function, f(S) has zero content only when S is disconnected? Like sequences mapped by continuous functions have zero content because they are indexed by integers which form a disconnected set?
• Nov 19th 2009, 12:19 PM
Jose27
If \$\displaystyle f\$ is not constant then yes, because if \$\displaystyle f(s)\$ has two elements say \$\displaystyle x<y\$ then, since \$\displaystyle f\$ is continous and \$\displaystyle S\$ is connected then \$\displaystyle f(S)\$ is connected which means \$\displaystyle (x,y) \subset f(S)\$ which means the content of \$\displaystyle f(S)>0\$.