the 8/2(2+2) crowd is almost as annoying as the people who claim that 9.99999... and 10 are different numbers and equally annoying as the people who can't grasp that dividing by zero is as invalid in algebra as it is in arithmetic send tweet
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Replying to @oe1cxw
Fun aside - in Algorithmic Information theory, you do want binary strings like 10.111111... and 11.0000... to be different, so a common convention to avoid confusion in Cantor space is to treat all binary reals as irrational. (Photo snapped from my copy of Downey and Hirschfelt)pic.twitter.com/ehO9WDVWUz
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Replying to @LargeCardinal
Interesting. Not sure if I'm missing something here, but 11.0000... obviously is rational. Therefore, as far as I understand this, it's not assuming that 10.1111... and 11.0000... are different. Instead, it's assuming that we never encounter such numbers.
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Replying to @oe1cxw @LargeCardinal
Okay, I read it again.. :) I'd need to know more about the problems studied here, but assuming that natural numbers are irrational intuitively screams huge bag of problems. I trust that it's not an actual problem in this case.
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Replying to @oe1cxw
Yeah, it's only an issue when you want to have a set of positive measure to show a binary string in ML-Random, or when you want to work on subshifts (sets closed under the 'shift left one' operation) and need everything to be distinct points without such identities creeping in.
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Replying to @LargeCardinal @oe1cxw
e.g. forbidden word problems. If 0.101111... and 0.110000... are the same, then it's difficult to say that the first avoids the forbidden word '000' if the second is in some way identical to it. (just an ex. off the top of my head)
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Replying to @LargeCardinal @oe1cxw
PS - this is probably the *least* weird thing about Algorithmic Randomness x-D
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Replying to @LargeCardinal
Excuse my ignorance. I've just read a bit on the topic on wikipedia. I'm mostly confused now. :) Most reals famously don't even have a finite description. So I have a hard time understanding how these questions even relate to those reals. If only I had more time. This looks cool.
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Replying to @oe1cxw
so, being honest with you - you can do just fine with these problems if you don't think of them as anything more than binary strings, i.e. you don't think of them as reals. >.< I'm very sorry if I've caused confusion...
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Replying to @LargeCardinal @oe1cxw
I think this is a case where being mathematicians, we state something to avoid confusion later, but instead cause even more confusion at the start. We're rather good at that...
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Confusion just means I know there's something to learn for me. That's usually good. :) So, when you say these objects are "binary strings", these strings are still potentially infinite in length, and for most of them there's no finite program to generate them, right?
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Replying to @oe1cxw
Exactly. Much of the study is for $\Pi^0_1$ classes, meaning there is some arithmetical function $\phi$, and we are saying $\forall x \, \phi(x)$ is true. After some work, this becomes equivalent to the usual interpretation:
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Replying to @LargeCardinal @oe1cxw
Some initial segment ('stem') \sigma, and the cone of all its extensions.pic.twitter.com/pyQw10Fv1R
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