Suppose there is a challenge that is rather hard, and has few answers. Is it OK to post a new challenge that is actually a part of the bigger and harder challenge? Of course, attributing the original author for inspiration is without question.
The new challenge may be considered a duplicate (as the answers can be trivially adapted just but cutting off big chunks of code). However, it can attract more users in a wider set of languages.
(I have in mind Is this Flow Free puzzle trivial? to be specific, but let's talk in general.)