Problem: If "Madonna fired her trainer because she slept with her boyfriend.", is "She slept with Madonna's boyfriend." correct?

Answer: yes

Problem: If "This book introduced Shakespeare to Ovid; it was a major influence on his writing.", is "It was a major influence on Shakespeare's writing." correct?

Answer: yes

Problem: If "John hired himself out to Bill to take care of him.", is "John hired himself out to Bill to take care of John." correct?

Answer:
no