# Negate a in b?

The opposite of a in b seems to be !(a in b) which looks clunky to me. I would prefer something like a not in b, but that doesn’t work.

Seems to me that a general rule would work well:

x not op y ≣ !(x op y)


Is there some way to achieve this?

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\notin expands to ∉, such as a ∉ b.

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 a in b can be written as a ∈ b with the mathematical symbol ∈. And the opposite of that, ∉ is available as an operator too, so you can do a ∉ b for !(a in b).

∈ can be typed with \in<TAB>, ∉ with \notin<TAB> in the REPL.

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Oooh, interesting. I shall give that a try.

It would be helpful if all such operators were “aliased” to normal words that one could type on a keyboard, however. I don’t know about you, but I don’t have a ∉ key on mine

What we need, I feel, is a way to create infix aliases or functions. Something like:

infix notin = ∉


Or even better, the ability to create our own infix operators.

You can type it on a normal keyboard in a Julia REPL or VS Code by typing \notin and pressing TAB.

But not in Atom.

The way to do this with infix operators is either a \notin<tab> b or !(a in b). But if you’re willing to give up infix, you can use the function form !in(a,b).

There are plugins for Atom and for all other popular editors nowadays to do LaTeX-like tab completion of Unicode math symbols.

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@stevengj I did not know that! This will come in very handy.

Thank you all for your help.

You can create your own infix operators. I have an example in New features coming in Julia 1.7 [LWN.net].