I hope this is valid:
multiply by -1 and add the result to the second give
I thought as much. This is from Apostol. I am sure that I have missed something. for example, , and these integrals are the upper and lower step function bounds. It's part of the integral definition.
I suppose because the upper step function is always above the lower step function that the difference must be more than zero.
Maybe I need to read it more carefully.