5 ms·

> the thunderbolt ↯ is commonly used for "not" or more specifically for dis-proof in this area and I don't think it's that common. At least, I don't recall see

> the thunderbolt ↯ is commonly used for "not" or more specifically for dis-proof in this area and I don't think it's that common. At least, I don't recall seeing it ever. Maybe it's used in non-English mathematics? Wikipedia mentions it's also used in electrolysis so maybe this new one is related to that somehow?

maze-le 5y ago
It's used in german mathematics education (secondary level), either to mark a contradiction in a proof or more generally to mark an erroneous statement.
- ruuda 5y ago
  Also in Dutch universities to mark a contradiction, especially in a proof by contradiction.
- dirkt 5y ago
  But I have never seen it to mark negation of a condition, that's usually done with a slash (as in ≠ ≮ ≯ ≰ ≱ ≴ ≵ ⊄ ⊅ ⊈ ⊉ ⊊ ⊋ ∉ ∌ ∄ ∦, you get the idea). So for "not a right angle" I'd have expected a "right angle" symbol with a slash through it.
  - r0uv3n 5y ago
    But how would you position the slash to get a somewhat easy to decipher symbol? To me, the right angle symbol seems to lend itself more to this unorthodox negation through the contradiction symbol than to negation through the normal slash.
  - maze-le 5y ago
    Funny enough, I've only seen it at the Gymnasium (secondary level) and not in the University a few years later -- then indeed the usual symbols were the 'slashed' relations like you've described, or the bottom symbol: ⊥ in logic. Maybe it's an idiosyncrasy of a certain subset of math teachers.
- deleted 5y ago
  [deleted]
qiskit 5y ago
Same. Never seen that symbol in my life. I've seen ¬, ~, !, etc used for not/negation in computer science, math, logic, etc. And some commenters said they used it to mark proof by contradiction, but why is there a need to mark it when you are showing it via proof? A canonical example of proof by contradiction is proving sqrt(2) is not rational. Never have I seen it marked with that symbol. Where would you even mark it? At the beginning with the assumption? Or at the end like QED?
- AaronFriel 5y ago
  Math degree holder from Iowa, yeah, I've seen and used it many times. The symbol is used when you reach the contradictory statement. Like "1 = 2". "By way of contradiction suppose P, then ..., thus ~P ↯. Therefore ..."
  - phogster 5y ago
    To me that reads: I throw your assumption into the GROUND!
  - nerdponx 5y ago
    I've actually always wanted a way to mark "the contradiction" once I've obtained it. Thanks!
- valtism 5y ago
  I was taught it in extracurricular mathematics in Australia. We were taught that it goes at the end of a contradiction proof once the contradiction has been found. We used to write it extra large, like lightning strike. I think of it like a proof mic-drop.
ratmice 5y ago
I believe I have seen it used as a symbol which indicates the discharge of an assumption, but never for "not".
ceh123 5y ago
It's the first symbol referenced for symbols used in proof by contradiction to show contradiction [0]. I know that's not exactly "not" or "disproof" but I think that might be what the poster was getting at. [0] https://en.wikipedia.org/wiki/Contradiction#Symbolic_representation https://en.wikipedia.org/wiki/Contradiction#Symbolic_represe...

maze-le 5y ago

It's used in german mathematics education (secondary level), either to mark a contradiction in a proof or more generally to mark an erroneous statement.

ruuda 5y ago
Also in Dutch universities to mark a contradiction, especially in a proof by contradiction.
dirkt 5y ago
But I have never seen it to mark negation of a condition, that's usually done with a slash (as in ≠ ≮ ≯ ≰ ≱ ≴ ≵ ⊄ ⊅ ⊈ ⊉ ⊊ ⊋ ∉ ∌ ∄ ∦, you get the idea). So for "not a right angle" I'd have expected a "right angle" symbol with a slash through it.
- r0uv3n 5y ago
  But how would you position the slash to get a somewhat easy to decipher symbol? To me, the right angle symbol seems to lend itself more to this unorthodox negation through the contradiction symbol than to negation through the normal slash.
- maze-le 5y ago
  Funny enough, I've only seen it at the Gymnasium (secondary level) and not in the University a few years later -- then indeed the usual symbols were the 'slashed' relations like you've described, or the bottom symbol: ⊥ in logic. Maybe it's an idiosyncrasy of a certain subset of math teachers.
deleted 5y ago
[deleted]

qiskit 5y ago

Same. Never seen that symbol in my life. I've seen ¬, ~, !, etc used for not/negation in computer science, math, logic, etc. And some commenters said they used it to mark proof by contradiction, but why is there a need to mark it when you are showing it via proof? A canonical example of proof by contradiction is proving sqrt(2) is not rational. Never have I seen it marked with that symbol. Where would you even mark it? At the beginning with the assumption? Or at the end like QED?

AaronFriel 5y ago
Math degree holder from Iowa, yeah, I've seen and used it many times. The symbol is used when you reach the contradictory statement. Like "1 = 2". "By way of contradiction suppose P, then ..., thus ~P ↯. Therefore ..."
- phogster 5y ago
  To me that reads: I throw your assumption into the GROUND!
- nerdponx 5y ago
  I've actually always wanted a way to mark "the contradiction" once I've obtained it. Thanks!
valtism 5y ago
I was taught it in extracurricular mathematics in Australia. We were taught that it goes at the end of a contradiction proof once the contradiction has been found. We used to write it extra large, like lightning strike. I think of it like a proof mic-drop.

ratmice 5y ago

I believe I have seen it used as a symbol which indicates the discharge of an assumption, but never for "not".

ceh123 5y ago

It's the first symbol referenced for symbols used in proof by contradiction to show contradiction [0]. I know that's not exactly "not" or "disproof" but I think that might be what the poster was getting at. [0] https://en.wikipedia.org/wiki/Contradiction#Symbolic_representation https://en.wikipedia.org/wiki/Contradiction#Symbolic_represe...