In the section “Additional Arrow Types” on page 65 there is a table describing different arrow styles. In the column Syntax examples are given in mermaid’s Markdown syntax.
Unfortunately some examples are rendered as symbols.
Like --> is rendered as right arrow “–>” and -- is rendered as long dash “—”.
Sigh, look like that got broken during layout adjustments for print release, thanks for raising, and thanks for purchasing, hope you’re enjoying the book!