JordiGH

JordiGH's avatar
JordiGH
🛡️ JordiGH@mathstodon-xyz.mostr.pub
npub17j8l...3mcf
Coder. Mathematician. Hacker-errant. You can also email me at jordigh@octave.org Please say something to me before following me! I'll have to carefully scrutinise your follow request if we haven't exchanged any words, but I'll probably approve it right away if you at least say hi. It's more work for me if you request a follow without any previous interaction. I'm married; no flirting please.
It's kind of fun, in terms of mathematical philosophy and history, how the symbol ∈ comes from Latin "est", meaning, "is", as in "x is an integer" or 𝑥 ∈ ℤ, but nowadays we interpret that as "x is in the set of integers". It kind of goes back to the origin of set theory when we thought that everything could be define with comprehension before Russell found contradictions like "set of sets that don't contain themselves" (I think "set of all sets" was due to Frege?") Anyway, back then being in a set was assumed to be the same as satisfying a predicate and they thought you would specify a predicate without reference to an enclosing set. So "Billy is a punk", or 𝐵𝑖𝑙𝑙𝑦 ∈ Punk was seen as equivalent. There was no need at the time to distinguish predicates from membership because there was some implied universe of all sets where each predicate would cut out a subset from. Only when we realised that predicates had to be in reference to an enclosing set in order to avoid contradictions, only then did we change the meaning of the ∈ symbol from "is" to "belongs to the set".