The phrase "a very complex one" is correct and usable in written English.
It can be used to describe something that is intricate or difficult to understand, often in contexts involving explanations, problems, or systems.
Example: "The issue at hand is a very complex one, requiring careful analysis and consideration from all parties involved."
Alternatives: "a highly intricate matter" or "an extremely complicated situation".
However, that there is a uniform semantics (even a very complex one) for generic claims, one moreover that "analyzes away" kind talk, is a strong empirical claim about language, one that does not receive strong support from current efforts to analyze generic claims.
The problem of star formation is a very complex one and its solution depends critically on knowledge of certain empirical data.
That bond is a very complex one.
Today the VED system is a general tax, and a very complex one.
Her character in the film, Grace, is a very complex one.
It is also a very complex one — and ultimately it is not clear, in our judgment, that it will play out this way.
I can have a very simple way of recording or a very complex ones.
They were asked to rate the tasks on the basis of their qualitative judgment guided by the checklist (Table 1) mentioned on a 5 level scale ranging from the simplest (1) to the very complex one (5).
He warns that "this highly technical regulatory guidance document is very complex". One example: if the guidance were adopted, a manufacturing change will trigger new dietary ingredient (NDI) status which, due to routine manufacturing processes, "essentially will put most botanical extracts into NDI territory". If so, this would add substantially to regulatory burden, and cost.
It's a very complex film – one which pays its audience the compliment of treating them like intelligent people who are prepared to engage intensely with his film.
It's just another technology, then, but it's a technology that has made certain things easier than they used to be and given rise to what we see as a somewhat dangerous fantasy that we can kill our way out of a very complex problem one bad guy at a time".
