[racket] Questions from a new user

Hello, all.  I just purchased Realm of Racket and am working my way through it.  Although I've been programming for 30+ years, most of that has been with procedural languages (MUMPS, FORTRAN and COBOL) on character-based medical information systems (i.e. reports, EDI and utilities).  This is one of my first attempts at GUI and functional programming and I'm enjoying it a lot.  Thanks to the creators of Racket and Scheme!

I'd like to ask some questions as I go through the book.

Is the book appropriate for learning Scheme in addition to Racket?  What % of the book deals with non-Scheme issues?  In the GUI version of Guess My Number many of the functions/procedures have an argument of w, which I understand to be world.  Why is world the argument instead of, say, interval?

Thanks, Steve    
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