(Copy Editor and mathematician speaking)
I, for one, allow these mixed constructions when editing the articles. I do know that it is not the best grammatical style, but not everything in math is easy to put down in proper English grammar. The two rules of thumb I use for these boundary cases is: Is the text clear to the reader? Can you easily make it grammatically correct?
For instance, the sentence
For matrix $A$, the equation $\rank(A)\geq5$ holds. is cryptic and long. A better option might be
For matrix $A$, we have $\rank(A)\geq5$. or
Matrix $A$ satisfies $\rank(A)\geq5$. I would be fine with
Matrix $A$ has rank at least 5. However, this gets complicated if you have more such expressions in a row, like in:
... which is defined as a non-real algebraic integer in modulus $>1$ whose
Galois conjugates except its complex conjugate are in modulus $<1$.
... which is defined as a non-real algebraic integer in modulus greater than $1$ whose
Galois conjugates except its complex conjugate are in modulus less than $1$.
I prefer the first option. This went through the AMS language editoral, as far as I remember, without any problem.