[luatex] How to get a \mid binary relation that grows in LuaTeX

[Hans Hagen]

On 11/15/2017 6:16 PM, Malte Dehling wrote:
> On Wed, Nov 15, 2017 at 03:16:45PM +0100, Hans Hagen wrote:
>> On 11/14/2017 1:43 PM, Malte Dehling wrote:
>>> I posted a question on tex.SE with the subject as title.  In short,
>>> there is a difference in how pdflatex and lualatex handle the expression
>>> $\left(a\mathrel{}\middle|\mathrel{}b\right)$.  Using pdflatex one gets
>>> symmetric spacing around the vertical bar while lualatex produces more
>>> space on the right.  See here for the question and an explanation in the
>>> answer:
>>>
>>> https://tex.stackexchange.com/questions/401234/how-to-get-a-mid-binary-relation-that-grows-in-luatex
>>>
>>> Is this a bug or intentional behavior?
>> A mixture.
>>
>> (1) middle behaves like a mixture of open and close and this was swapped so
>> that's a bug
>>
>> (2) but ... luatex provides control over the spacing and as you inject a rel
>> noad you get twice the spacing but you can tweak that with
>>
>>      \Umathopenrelspacing \textstyle0mu
>>      \Umathcloserelspacing\textstyle0mu
> 
> Am I correct in assuming that this would have unintended side effect in
> many other equations, not just spacing of \middle (and maybe \left and
> \right?)

sure but then, using an empty \mathrel{} in there is kind of bad .. 
better add some explicit muskip then

>>
>> (3) the good news is that you can do this:
>>
>>      \left( a \Umiddle class 5 | b \right)
> 
> Heel erg bedankt!  I'll use this since I only need to compile with
> lualatex.  For the record, Enrico (egreg) posted an answer to my
> question on tex.se, based on your reply, which works in both pdflatex
> and lualatex.
> 
> Best,
> 


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