[zeteo]

> (C) the thunderbolt ↯ is commonly used for "not" or more specifically for dis-proof in this area

Any examples?

[HuangYuSan]

I believe in German (possibly also other languages) the thunderbolt ↯ is commonly used to mean "this is a contradiction" in a mathematical proof, equivalently to in English a kind of ⋕ rotated by 45° or the symbol ※. The symbol ⟂ on the other hand means "false" and is used in particular in formal logic.

[froh]

Yes and no.

Yes, we indeed used and afaict still use the thunderbolt for contradiction in my German university.

However "perpendicular" and "bottom/falsum" are two different Unicode codepoints with very similar glyphs.

https://en.m.wikipedia.org/wiki/Up_tack

[contravariant]

I've seen it used for contradiction. Though that's not the same thing as 'not' and I can't think of why you'd combine this with orthogonality.

[hedora]

If the thunderbolt means not, and the right angle is displaying the x and y axis, then this symbol could be a pun for "not a function".

[firstcommentyo]

High school physics and math as a major. I could scan you my scripts and papers if you're interested.....no won't. ;-D

But maybe "commonly used" was maybe the wrong term. More appropriately: "sometimes" or "by some".

[renewiltord]

Where in the world? I’ve never used it despite similar background. Perhaps regional?

[IshKebab]

I have never seen it used as not once in maths or physics. "extremely rarely" perhaps.

[mywittyname]

To be fair, there are lot of math symbols out there.

http://mirrors.dotsrc.org/ctan/info/symbols/comprehensive/sy...

There are lots of examples of the lightning bolt in there. In fact, under ulsy Contradiction symbols, there are four variants.

I also noticed the exact symbol being discussed is listed under "Angles".