Hatcher’s Algebraic Topology unfortunately hadn’t been written when I studied the subject in grad school, but a few years ago I participated in a meetup that went through about half of it. I wrote up notes on things I puzzled over, or just observations I found helpful. Here they are. Besides the homology group mentioned in the title, some other tidbits: a figure to elucidate the calculation of the fundamental group of the complement of the Alexander Horned Sphere, and more details for the intuitive proof Hatcher sketches of Poincaré duality.
The Peloponnesian War
Filed under History Book Club, Reviews
Socrates, Bad Guy
Another post from the History Book Club. Continue reading
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Gracefully Insane
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Topics in Nonstandard Arithmetic 9: Tricks with Quantifiers
Every specialty has its tricks of the trade. They become second nature to practitioners, so they often don’t make it into the textbooks. Quantifiers rule in logic; here are some of the games we can play with them. I’ll start with tricks that apply in logic generally, then turn to those specific to Peano arithmetic.
Filed under Peano Arithmetic
The Second French Revolution
Another post from the History Book Club. Continue reading
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Topics in Nonstandard Arithmetic 8: Extensions and Substructures
Substructures and extensions loom large in math: subgroups, subrings, extension fields, submanifolds, subspaces of topological spaces… So too in the model theory of PA.
Filed under Peano Arithmetic
Nonstandard Models of Arithmetic 24
MW: Indicators: we don’t need to discuss these, to prove the Paris-Harrington theorem. But I think they offer valuable insight.
Filed under Conversations, Peano Arithmetic
The Decision to Drop the Bomb
Another post from the History Book Club.
(Why ‘atomic bomb’ rather than ‘nuclear bomb’? See this post.)
Filed under History Book Club, Physics, Reviews
The Making of the Atomic Bomb
For a few years, I belonged to a history book club. Unlike many book clubs, we didn’t all read the same book. Instead, we’d pick a topic for the next meeting, at which the participants would each give short presentations on books of their choosing.
Recently I ran across my write-ups. As the internet has yet to run out of space, I thought I’d post them. I begin with two on the atomic bomb.
(Why ‘atomic bomb’, rather than ‘nuclear bomb’? See this post.)
Filed under History Book Club, Physics, Reviews