Another bugs? \advance\prevdepth, \ifnum

[Hans Ginzel]

	Dear TeX implementors,

   I realised another unexpected matter. Try

	Somthing.\par
	\shothe\prevdepth	% OK, 1.9444pt
	\prevdepth=4pt		% OK
	\advance\prevdepth by\baselineskip
	% you can't use `\prevdepth' after \advance.
	% But:
	\newdimen\tempdim
	\tempdim=\prevdepth
	\advance\tempdim by\baselineskip
	\prevdepth=\tempdim	% OK

   Why is possible to assign a value to \prevdepth and to \advance this
register? Because there is a test in the section 1237 of tex.web if the
command after \advance is a register, but \prevdepth is set_aux (209).

   I consider this as bug. If it is knowen, I am sorry. But where to
search for knowen bugs?


   Three years ago I submited to our local group yet another suspicious
matter. Nobody gave me a seriose answer.

	\edef\a{\ifnum1<2\else\fi}\show\a	% macro: \relax
	\edef\b{\ifnum1<2 \else\fi}\show\b	% like \empty

   But this is probably autors goal. Can you explain, please?



	Best regards

					Hans Ginzel
--
Faculty of Mathematics and Physics, Charles University, Prague