The phrase "a primary difficulty in" is correct and usable in written English.
It can be used when discussing a main challenge or obstacle related to a specific topic or situation.
Example: "A primary difficulty in implementing the new software system is the lack of training for staff."
Alternatives: "a major challenge in" or "a key issue in".
A primary difficulty lies in defining a treatment that will effectively destroy disseminated tumor cells without significant toxicity to the patient.
In natural systems, a primary difficulty to exporting more sophisticated tools in their integrity, such as transgenesis and genome editing, to a wide range of organisms resides in the endless differences in the specificities of each model system.
The primary difficulty in the identification of Hammerstein nonlinear systems (a static memoryless nonlinear system in series with a dynamic linear system) is that the output of the nonlinear system (input to the linear system) is unknown.
This is exactly the relationship we would expect for a set of cDNAs that are not truly full-length, since the primary difficulty in producing full-length cDNAs is obtaining the full 5'-end.
The primary difficulty in diagnosing infections by Penicillium, due to its rarity, is a low clinical suspicion.
The primary difficulty in creating computers is making logical circuits without wires crossing; wires cannot cross separate from each other in a 2-d world.
"The primary difficulty in staff planning at this time was the fact that neither the field nor Headquarters possessed detailed information on military figures in Iran.
But insiders say the primary difficulty in prosecuting Mr. Milosevic for Kosovo will be to establish the credible links between Mr. Milosevic and the looting, raping and killing attributed to the Yugoslav forces on their rampage through Kosovo.
The primary difficulty in applying the Poisson approximation is the determination of the optimal parameter μ n, which is higly dependent on the structure of the pattern Λ.
