standard usage of O(x^3) can be confusing
Regarding Russell O'Connor's observation that ...
"the notation is a little confusing.
f(x) = 5x + 6x^2 + O(x^3)
f(x) - 5x - 6x^2 $isin; O(x^3)
It is actually the author that chooses to write one versus
the other, not MathML.
In this case, O(x^3) would appear to be one of the building
blocks (needed by both) and it is up to the author to use it effectively.
A perfect example why would be to consider writing a web page that is
discussing the difference between these two notations.