Signed-off-by: Jim Pryor <profjim@jimpryor.net>
* The [Complete Racket Reference Manual](http://docs.racket-lang.org/reference/index.html) defines the core Racket language and describes its most prominent libraries. The Racket Guide is friendlier; though less precise and less complete.
* The Scheme language is standardized; the various implementations of the
-language usually adhere to what's published in the current standard and on
+language usually adhere to what's published in the current standard and add on
different handy extensions. The first standard was published in 1975. A
revision was published in 1978 called "The revised report on Scheme, a
dialect of Lisp." Thereafter, revisions of the standard were titled "The