Sagittarius works with library even toplevel expressions are belong to a library
named "user". Here I list up all R6RS libraries. Some libraries contain
the same procedure ie. assoc which is in (rnrs (6)) and
(srfi :1 lists). In this case I will put a pointer to other library's
section.
If library specifies its version, Sagittarius, however, ignores it. This behaviour may change in future.