Useful link with explanation of subtyping in Kotlin?

[MeAmAnUsername]

Todo

• Decide where to put link
• Link to this blog post: http://www.natpryce.com/articles/000818.html
• Describe differences with PIE
  • PIE top type is nullable, while Kotlin any type is not
  • more...?

Location
Explanation of subtyping should be clear enough on its own (that is to say, the intention is that the documentation on subtyping in the PIE DSL is clear enough, I don't know if it is at the moment), but maybe a note like "parallels with subtyping in Kotlin" might help, or mention it in background somewhere.