[racket] where are lib locations given?

hello,

where do i find the required lib when using a form, such as (struct
...)?

neither the guide, under

5 Programmer-Defined Datatypes
http://download.racket-lang.org/docs/5.2/html/guide/define-struct.html

nor the manual, under

4 Structures
http://download.racket-lang.org/docs/5.2/html/reference/structures.html

tell where to take the lib from.

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