They create a generous space as they swing open, and for the same reason are difficult to close manually.
Thus, manufacturing antennas in large quantities for experimental reasons is difficult and even impractical.
The widening of the ventricles are pronounced and sometimes the distinction between widening of ventricles and hydrocephalus of other reasons is difficult.
Looking for reasons was difficult, due to differences in data collection: UK income is recorded for families, Sweden's for individuals.
Some of the reasons are difficult to address since they are inherent features of a patent (e.g. low image quality, typos and OCR conversion errors), others (e.g. Markush structures) offer opportunities for future developments.
Imprinted gene expression status in the healthy adult human has for obvious reasons been difficult to characterise.
The reasons are difficult to explain and in-depth exploration of associated socio-economic and/or psychological factors is required.
Connecting individuals to systems is hard, which is one reason change is difficult.
These things are easy to see with data and a little reason; what is difficult is changing the culture.
