core.thread vs std.concurrency - which of them to use?

[Victor L Porton via Digitalmars-d-learn]

When to use core.thread and when std.concurrency for 
multithreading in applications? Is one of them a preferred way?

Are function literals deprecated?

[Victor L Porton via Digitalmars-d-learn]

I am writing a book about D (I already have 150 pages).

Are function literals considered deprecated in regard of using 
delegates instead?