Oh no! At first I thought this paper was just bing silly/clever with `⟅⟆ : Bag` (it looks like a bag 💰 haha), but then I realised this is actually a thing! Unicode calls them 'bag delimiters'… 😱
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And so followed my first hunt for the history of a character's introduction into unicode: unicode.org/L2/L2003/03410 - no idea what the history is of these characters in mathematics though... 🤔
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Apparently they come from Squiggol!
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Replying to @Teggy and @brendanzab
Indeed I do. They were whiteboard notation in the Squiggol community in late 80s, early 90s. @asajeffrey and I put them in the St Mary's Road symbol font. I guess Unicode picked them up from there.
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Also known as the "Bird–Meertens formalism":
> Facetiously it is also referred to as Squiggol, as a nod to ALGOL, which was also in the remit of WG 2.1, and because of the "squiggly" symbols it uses.
⟅😂⟆
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Replying to @samthecoy and @FakeUnicode
This was the paper that led to the goose chase for squiggolly bag symbols: S-C. Mu, H-S. Ko, and P. Jansson. "Algebra of programming in Agda: dependent types for relational program derivation" iis.sinica.edu.tw/~scm/2009/alge
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Indeed I do. They were whiteboard notation in the Squiggol community in late 80s, early 90s. and I put them in the St Mary's Road symbol font. I guess Unicode picked them up from there.
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\Lbag and \Rbag in the stmaryrd LaTeX package, which is copyright 1991-1994. Calls itself "for theoretical computer science".
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Apparently the sample specimens were taken from those ancient horrible LaTeX to HTML renderings, that generate cursed aliased gifs for all "strange" text. The only way to make it worse would have involved a fax machine.
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