Paper/PDF table of contents shows "Intro" instead of chapter title for chapters 6 and 7.

This issue applies to both the paper book (purchased last year) and the PDF (https://rust-exercises.com/100-exercises-to-learn-rust.pdf).

The table of contents at the start of the book shows the wrong title for chapters 6 and 7. It shows "Intro" for both of them. This appears to be because the introductory section of those chapters has the heading "Intro" instead of the chapter title.