The phrase "a difficult instance for" is correct and usable in written English.
It can be used when discussing a specific situation or example that presents challenges or complications for someone or something.
Example: "This case presents a difficult instance for the legal team, as they must navigate complex regulations."
Alternatives: "a challenging situation for" or "a tough case for".
Interestingly, the most difficult instances for the latter three models appear to be those with the equal number of facilities and customers.
It is very difficult, for instance, for my team to make appointments with Alex, a young homeless woman with a criminal record and without a mobile phone, who suffers horrific hallucinations of abuse.
That makes it difficult, for instance, for women who need maternity leave.
Its enormous biochemical complexity [ 440] makes detailed, microscopic modeling approaches a difficult task while, for instance, its response to exerted forces and their use for environmental sensing makes them physically very appealing to study [ 440, 441] (Section 3.3.6).
Using W4 (the smallest forbidden subgraph for monopolar graphs) as a cutting plane also helps little, solving one more instance, but might be useful for difficult instances with long running time.
PMS5 [ 7] computes the common d-neighbors of three l-mers using integer programming formulation, which is an efficient algorithm for solving the difficult instances of PMS: (21, 8) and (23, 9).
Human minds are skilled at recognizing spatial patterns easily distinguishing among human faces, for instance but this is a difficult task for computers, which must process information sequentially, rather than grasping details overall at a glance.
Getting a divorce would be difficult, for instance, if the couple lived in or moved to a state that didn't recognize their union.
(Rural) As with other health care providers, retaining a rural CAM workforce can also be difficult, for instance, "...there was a wonderful man up here but he decided to go because his wife had been bitten by so many ticks".
Similar to highly heritable psychiatric phenotypes, the molecular elucidation of body weight regulation based on data from GWAS has proven more difficult than, for instance, for body height, inflammatory bowel disease or specific complex neurological disorders.
