[R6RS] issues in document/lex.tex

[William D Clinger]

While reviewing document/lex.tex, I noticed two major
issues:

1.  The extensive use of "S-expression" instead of
"external representation" seems like a step backwards.
The R4RS and R5RS never use "S-expression", and this
reflects a deliberate decision to rid ourselves of the
historical connotations of that term.

2.  The current draft of lex.tex says "The _nan.0 and
-nan.0 literals represent the NaN that is the result
of (/ 0.0 0.0) and may represent other NaNs as well."
I am pretty sure that the editors never agreed to make
-nan.0 represent the same NaN as +nan.0.  This change
runs counter to the more obvious use of -nan.0 to
represent NaNs whose sign bit is 1 instead of 0.
Note also that that interpretation of -nan.0 was
requested by at least one person during the discussion
of SRFI 77.

Will