I don't know first thing about math, but even I find that the classical definition (i.e. that find in the CLRS book) is pretty straightforward: given an input b

I don't know first thing about math, but even I find that the classical definition (i.e. that find in the CLRS book) is pretty straightforward: given an input big enough, the running time will be at most that of a multiple of function g(n) if f(n) = O(g(n)), where f is the function that describes the algorithm's running time.