Chol HaMoed is the only time I have to learn a little more earnestly, and it is very helpful to write in order to learn things. Would it be very harmful for me to write, then, or could I risk it under the circumstances?
Writing for the sake of ones study, if helps - is permitted and no risk is involved. The reason for this is that on Chol Hamoed anything that might be lost if it is not done (Davar Ha'aved) is permitted, therefore Rabbi Avraham Shapira ZT"L said that there is nothing more Davar Ha'aved than Divrei Torah - Torah study. Rabbi Yitzchak Grinblat