The phrase "asserts exactly" is correct and usable in written English.
It can be used when you want to emphasize that someone is stating something with precision or certainty.
Example: "The report asserts exactly what the findings indicate, leaving no room for misinterpretation."
Alternatives: "states precisely" or "declares accurately".
That's why I was startled to see my fellow Economix blogger Jared Bernstein assert exactly the opposite.
It seems to me that, sometimes with great pain, you've gone right through this book asserting exactly what your heart believes, and has learned to believe.
On the left are the Modern Monetary Theory types, who assert exactly what the austerians like to claim, falsely, is the Keynesian position – that budget deficits never matter (except for their direct effect on aggregate demand).
It is thus possible for two individuals in different worlds to assert exactly the same propositions, and yet differ with respect to having asserted a true proposition.
If, within a world, two individuals assert exactly the same propositions, then they are exactly alike vis-à-vis having asserted a true proposition: the one asserted at least one true proposition if and only if the other did.
In fact, he asserts, that is exactly why all of us have gathered in Nepal in the first place.
As it is now conventionally formulated, it asserts that there is exactly one parallel to a given line through a given point.
In discussing Patty Bloomstine of Erie County, Pennsylvania, Zito asserts that Bloomstine is "exactly the kind of voter who was at the top of Hillary Clinton's persuasion-target list during the 2016 campaign".
It does not exactly assert that "there ain't no such animal," but it is announced that the breed of "Northern Tibetan Hunting Dog" has yet to be entered on the social register of the doggy sort.
