(1) Leave out the first step and do it yourself. (2) When it is k, the left end is:

1+ 1/2+ 1/3+...+ 1/(2^k- 1)

When k+ 1, the left end is:

1+ 1/2+ 1/3+...+ 1/(2^k- 1)+ 1/(2^(k+ 1)- 1)

Comprehensive (1)(2) Obtain the certificate.