\in\not vs \notin

[OliverEvans96]

Hello,

I've found a discrepancy between two ways to write ∉ at the REPL Julia v1.6.0-beta1 on Arch Linux.

Both are recognized at the help?> prompt and suggested to be typed the same way, but only \notin has methods - \in\not is undefined.

Here's a summary of the differences

Typed	Displayed	Raw bytes (Vector{UInt8})	help?> typing hint	Number of methods
\notin<tab>	∉	[0xe2, 0x88, 0x89]	"∉" can be typed by \in<tab>\not<tab>	2
\in<tab>\not<tab>	∉	[0xe2, 0x88, 0x88, 0xcc, 0xb8]	"∉" can be typed by \in<tab>\not<tab>	0

I'm curious whether others observe the same issue on other systems or Julia versions.

Cheers,
Oliver

[JeffBezanson]

These are considered different names under the unicode normalization that we use. Is there a normalization form that equates them?

[mbauman]

Either way, it looks like our help hint is wrong for \notin. I'm guessing that's how you stumbled across this issue?

[OliverEvans96]

Yes, I suppose it was. I didn't know how to type that character, so I pasted it in help?> and got bad advice

[OliverEvans96]

All of the above also seems to apply to other "not" symbols. e.g.

help?> ≠ #\ne
"≠" can be typed by =\not<tab>

help?> ≉ #\napprox
"≉" can be typed by \approx<tab>\not<tab>

[clason]

Hmm, it works here (julia 1.6.0-rc1 as well as 1.7.0-DEV.606, macOS Intel, iTerm2) \in<tab>\not<tab> gives ∉ (and similarly for =\not<tab>).

The difference between the two methods is that the first directly inserts the character, while the second needs to delete the \in you've inserted first. Maybe your terminal can't handle the necessary terminal control codes? Which terminal are you using?

[clason]

@OliverEvans96 ☝️

(I forgot that editing doesn't notify people...)

[OliverEvans96]

I'm using gnome-terminal

[clason]

Can you test a different one (kitty, alacritty, pangoterm)?

[mbauman]

Hunh, that's odd. Here's what I see on 1.6.0-rc1 and 1.7.0-DEV.606, macOS/x86/iTerm2 Build 3.4.4:

help?> ∉ # \notin
"∉" can be typed by \in<tab>\not<tab>

search: ∉

  ∉(item, collection) -> Bool
...
julia> ∉ # \in\not
ERROR: UndefVarError: ∉ not defined

On 1.5 the hints match how I wrote it.

[clason]

Oh, I also get the not defined; I assumed that was intentional. (I was testing on the standard REPL, not help mode.) This indicates that these are two different unicode chars (single vs. composite, with not all terminals understanding the latter).

[mbauman]

Aha, I bet the hints changed in #36382, where we use NFD normalization to look up the latex completion. Watch out, it's what GitHub apparently uses, too. Julia source code uses NFC. The former normalizes \notin to the combining characters; the latter does not.

julia> codeunits(REPL.REPLCompletions.latex_symbols["\\notin"])
3-element Base.CodeUnits{UInt8,String}:
 0xe2
 0x88
 0x89

julia> codeunits(Unicode.normalize(String([0xe2, 0x88, 0x89]), :NFC))
3-element Base.CodeUnits{UInt8,String}:
 0xe2
 0x88
 0x89

julia> codeunits(Unicode.normalize(String([0xe2, 0x88, 0x89]), :NFD))
5-element Base.CodeUnits{UInt8,String}:
 0xe2
 0x88
 0x88
 0xcc
 0xb8