[luatex] Proposal for extensible arrows

[Will Robertson]

Hi Hans,

> On 13 Feb 2016, at 11:47 PM, Hans Hagen <pragma at wxs.nl> wrote:
> 
> we already have Uhextensible (and a whole bunch of extras) ... it all depends on what the font provides; the gyre fonts do have extensible arrows already

Oh, I apologise — I’m still using the TL2015 version of LuaTeX and hadn’t caught this news. The \Uhextensible primitive is exactly what I was thinking of (and the other new maths primitives look good as well — thanks!).

Whether \Uvextensible is really necessary is an open question — I’d say that it’d be "good to have” but doesn’t solve as much of a need as the h version.

> (It is unlikely that the math engine will be touched much, at least nto before 0.95. Quite some code was overhauled - a better split between old and new font as well as some detailed control over extensibles, delimiters etc. - some was added for completeness even if it could be done otherwise. An upcoming TB article will explain/show some.)

Looking forward to it, thanks again.

Cheers,
Will