For the following question when I am trying to prove the n = k+1 case am I allowed to substitute it in the first line of the question and also in the second line of the question?
What I am trying to say is am i allowed to assume:

For the following question when I am trying to prove the n = k+1 case am I allowed to substitute it in the first line of the question and also in the second line of the question?
What I am trying to say is am i allowed to assume: