Re: why does lily prints both a natural and sharp sign?

[Janek Warchoł]

>> I do not know it is "standard typesetting rules" that accidentals _at
>> the key signature_ implies extra naturals, though.
>> Some people have valuable (books) references, such as Ted Ross or
>> Gardner Read, maybe they could check the "rules" concerning key
>> signature and extra naturals.
>>
>> I am not aware of (free) online version of music typesetting rules
>> (conventions), but again, maybe other users have advice.
>
> I've looked at Ted Ross, Kurt Stone, Gardner Read and Elaine Gould and can't
> find any explicit mention of this.

AFAIK this was a common practice in XIXth century engraving (a period
that LilyPond tries to mimic), but it is considered now obsolete, at
least by some people
(http://icking-music-archive.org/lists/sottisier/sottieng.pdf page 6).

HTH,
Janek