'greatly difficult' is correct and usable in written English.
You can use this phrase when you want to emphasize that something is very difficult. For example: "Learning a new language can be greatly difficult."
The deployment of centrifuge plants is worrying because verification of the absence of such a programme is very difficult, greatly complicating any denuclearisation process.
In the Facebook message, his mother said: "The ongoing support and outpouring of love for Stephen will help greatly at this difficult time, in the same way as it helped Stephen throughout his journey.
Announcing Stephen's death, his mother wrote that "her heart is bursting with pride but breaking with pain for my courageous, selfless, inspirational son", and that the "ongoing support and outpouring of love for Stephen will help greatly at this difficult time, in the same way as it helped Stephen throughout his journey".
"The ongoing support and outpouring of love for Stephen will help greatly at this difficult time, in the same way as it helped Stephen throughout his journey.
Since the size of different skin components may vary greatly, it is difficult to define an appropriate structuring element for closing operation which can remove all unrelated skin tissues and keep the epidermis area unchanged.
The estimated energy scenario (2015 2030) is based on several factors that are unfortunately greatly simplified and/or difficult to verify where the latter is mainly caused by an almost total lack of useable data.
The army troops encountered few Japanese but were greatly slowed by difficult terrain and stopped short of the coast for the night.
Despite having no contact for years, Charice tells "Oprah: Where Are They Now?" that her father's death affected her greatly and heightened difficult personal issues she had been struggling with, like her sexuality and gender identity.
