Mind also updating the about.md file?

What's the difference between the two? Where does the introduction show and where does the about show?

What's the difference between the two? Where does the introduction show and where does the about show?

Described here: https://exercism.org/docs/building/tracks/concepts

about.md: provide information about the concept for a student who has completed the corresponding concept exercise to learn from and refer back to (required)
introduction.md: provide a brief introduction to a student who has not yet completed the corresponding concept exercise (required)

More comprehensively:

After completing the corresponding Concept Exercise (otherwise known as "learning" a Concept), the Concept page will show the contents of the about.md file instead of the introduction.md file. The about.md file should provide students with comprehensive information on what they need to know to be fluent in the concept. At a minimum, this file should contain all information that is introduced in the Concepts' introduction.md document.

They determine what is displayed here: https://exercism.org/tracks/java/concepts/booleans

Done with about.md, also added => arrows here like the about.md for consistency.