## Metric

Hi All;
I need The solution of the following question"
Let $X$ be a set of measurable functions from a measurable set $I$ to $\Re$ , then we defined a metric $d$ on $X$ By
$d(f,g)=\inf_{\varepsilon\longrightarrow0}(\varepsi lon+m(t:|f(t)-g(t)|\geq \varepsilon))$,
Then prove that d is a metric on $X$.