Improve support for logical symbols

[dankamongmen]

Hello again! I've been using U+21AE LEFT RIGHT ARROW WITH STROKE (↮), and Gentium has made the strange IMHO choice of placing the stroke on the far right of the glyph.

It's not the only font that does this -- I see similar behavior from FreeSerif (though only in italic), Cousine, Charis SIL (all forms), and others. Nonetheless, this seems incorrect. Proper glyph formation, with the stroke in the center, can be seen in Asana Math, DejaVu, Linux Libertine, JetBrains Mono, and others.

Indeed, in my browser, https://www.compart.com/en/unicode/U+21AE renders with the stroke far off to the right, but it gets https://www.compart.com/en/unicode/U+21CE correct:

↮
⇎

so this clearly isn't a problem with just Gentium, but i do think it's a definite bug. left right arrow with stroke is clearly intended as a foil to left right arrow. the latter is a symbol for tautology (https://en.wikipedia.org/wiki/Tautology_(logic)) whereas the former is a symbol for exclusive-or (https://en.wikipedia.org/wiki/Exclusive_or).

perhaps you know something i don't, of course. otherwise, it would be great if the stroke could be in the middle. actually, i see that this affects U+21CE LEFT RIGHT DOUBLE ARROW WITH STROKE in gentium also.

if this needs be fixed in some Ur-font from which gentium inherits, let me know, and i'll go report a bug on them, too.

(btw i noticed that my Debian machine only has 6.102; i filed a bug to upgrade the debian package to 6.200)

[dankamongmen]

i'm looking forward to using the new logical symbols from gentium 6.2, btw! this table will look a lot better

[dankamongmen]

it sure does!

it would be great to get U+22BD NOR and U+22BC NAND to go along with OR and AND! ⊽⊼

[dankamongmen]

ooooh, i was able to fake U+22BD NOR and U+22BC NAND with $\overbar{\mbox{X}}$, so now my table is perfect (presentation-wise anyway) except for U+21AE.

[jvgaultney]

The reason for this is that 21AE isn't in our fonts - so you're getting some fallback font. But since we do support other similar symbols that are used together, as in:

it would make sense for us to support 21AE - and 22BD, 22BC.

If there are others that are highly likely to be used together like this let me know. Thanks!

[dankamongmen]

yep, i'm using each of those symbols already, alas (see table in #29 (comment)).

⇹ (U+21F9 LEFT RIGHT ARROW WITH VERTICAL STROKE) would also satisfy my needs.

The reason for this is that 21AE isn't in our fonts

well, i'm embarrased. feel free to close this if you'd like, or keep it open as a request to implement a few more of these arrows, and NAND, and NOR =]. retitle if you'd like.

[jvgaultney]

Thanks!

[jvgaultney]

Hmmm. If you need both U+21AE and the vertical stroke counterpart (U+21F9) then wouldn't you also need U+21F7 and U+21F8? Do you really need both U+21AE and U+21F9?

[dankamongmen]

Hmmm. If you need both U+21AE and the vertical stroke counterpart (U+21F9) then wouldn't you also need U+21F7 and U+21F8? Do you really need both U+21AE and U+21F9?

nope, i only need one! i was just saying that if 21F9 was available, it would also suffice. i agree that 21ae makes more sense given the glyphs you're already supplying.

[jvgaultney]

Got it thanks