The Great Matthes Crest Cluster

Jul. 22nd, 2017 12:16 am
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[personal profile] joshua0
rope running between flakes on Matthes Crest

On Saturday (that is to say, July 15th), Josiah, Liz, and I went for an attempt on the Matthes Crest traverse from south to north. It was a total mess; in my book, it falls just barely short of an epic, but it certainly crosses the line over into being a total cluster. We got in a decent ways over our heads, made a mess of basically the whole route, and had a really long day. Remarkably, almost the entire day was still fun. Here is, more or less, how it happened.

--- More (3483 words) --- )
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(no subject)

Jul. 20th, 2017 06:22 pm
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[personal profile] jcreed
Took the train back home. It was a bit annoyingly delayed due to a freight train ahead of us, which meant that I got back in the middle of rush hour instead of an hour before, so the MTA trains in turn were pretty fucked, so I had a long, hot walk back home from the train station about 4 stops away that I decided to give up from.
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CMUQDB #4478

Jul. 19th, 2017 04:00 am
[syndicated profile] cmubash_feed
< mrwright> there's no chance of privilege escalation if all the privileges start out as high as they can go.

(no subject)

Jul. 17th, 2017 05:49 pm
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[personal profile] jcreed
On a train to pittsburgh.

My self-imposed agda-exercise for the train trip was to prove that assuming polymorphic functions
f : {C : Set} → (A → C) → (B → C) have the free theorem you expect them to from parametricity (namely (g : A → C1) (k : C1 → C2) → k ∘ (f g) == f (k ∘ g)) then

((C : Set) → (A → C) ≃ (B → C)) ≃ (B ≃ A)


Interestingly, it was very easy to show

((C : Set) → (A → C) → (B → C)) ≃ (B → A)


and only mildly more challenging to show

((C : Set) → (A → C) ≃ (B → C)) → (B ≃ A)


but the equivalence-of-equivalences was pretty tricky. I succeeded with a few hours to spare, though! I did it by separating out the functions from the is-equiv property they satisfied, and taking advantage of the mere-proposition-ness of is-equiv.

Huh, and I didn't even need univalence, it looks like. Except for using function extensionality all over the place --- but as we all learned in HoTT kindergarten, that follows from the existence of an interval type also.
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(no subject)

Jul. 15th, 2017 08:41 pm
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[personal profile] jcreed
17776 ended today. Sad, but nice to have a contained little story instead of a sprawling Joycean glorious mess like Homestuck.
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(no subject)

Jul. 14th, 2017 08:49 am
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[personal profile] jcreed
Having severe problems getting about 30G of files onto this hard drive without rsync slowing to a crawl at some point during the transfer and basically locking up my machine. Hard to tell whether is hardware or OS problem; trying to format it ext3 or ext4 *now* seems to take forever, although I swear I succeeded at an ext4 format once.
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(no subject)

Jul. 13th, 2017 08:47 am
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[personal profile] jcreed
Popped over to B&G to get a new mouse (my favored years-and-years-old one is finally having debouncing failures and registering double-clicks when I single click about 20% of the time) and an external hard drive for making backups.
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CMUQDB #4477

Jul. 15th, 2017 12:54 am
[syndicated profile] cmubash_feed
* nwf reading the parisc manual, send help
< nwf> Oh god
< nwf> Since a branch instruction may be executed in the delay slot of another branch instruction, an interesting case arises because of the way the privilege level changes are defined to take effect.
< labbott> > delay slot
< lroop> so PA-RISC did have delay slots?
<@kvincent> lroop: only schlong
< lroop> "schlong delay slot" sounds like some terrible comparch themed porno
< labbott> D:
< nwf> I,I bubbles in the pipeline
< lroop> followed by "Two Instructions, One Pipeline - The Hyper Threading Edition"

(no subject)

Jul. 11th, 2017 10:00 pm
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[personal profile] jcreed
Somehow just proving that this big nasty mutually recursive datatype is a set (as opposed to a space with higher path structure) is trickier than I thought.
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(no subject)

Jul. 10th, 2017 08:16 am
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[personal profile] jcreed
Saw a talk over at Cooper by Just van Rossum, Guido's little brother, who makes fonts and animations and things. Fun stuff.

Really falling in love with 17776, a story about space probes and football and lunchables and what it means to be human.
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(no subject)

Jul. 9th, 2017 10:28 pm
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[personal profile] jcreed
Made some progress proving the conjecture from yesterday.
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Jeff Grafton

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