Lebesgue integration quesetion
I have started studying Lebesgue integration and I have a question regarding the Lebesgue integral:
In the wikipedia entry of "Lebesgue integration" they define the Lebesgue integral as:
Let be a positive real-valued function.
where . The Lebesgue integration notes that I am studying defines the Lebesgue integral of a positive measurable function as I want to know if this wiki definition is equivalent to the integral constructed from simple functions, if so how can this be easily shown?