Hi all, I am having difficulties understanding Riesz basis for non orthogonal bases and I am stuck on the following problem. The definitions are abstract to me and I’m not sure how to go about solving the problem.

From Wikipedia, it seems that I should be be proving condition #2 (c and C correspond to A and B in the definition above):

I would greatly appreciate any help.

From Wikipedia, it seems that I should be be proving condition #2 (c and C correspond to A and B in the definition above):

I would greatly appreciate any help.