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# Tag Archives: theory

## Competitive Programming in Haskell: modular arithmetic, part 2

In my last post I wrote about modular exponentiation and egcd. In this post, I consider the problem of solving modular equivalences, building on code from the previous post. Solving linear congruences A linear congruence is a modular equivalence of … Continue reading

## Competitive Programming in Haskell: modular arithmetic, part 1

Modular arithmetic comes up a lot in computer science, and so it’s no surprise that it is featured, either explicitly or implicitly, in many competitive programming problems. As a brief aside, to be good at competitive programming it’s not enough … Continue reading

## Competitive Programming in Haskell: primes and factoring

Number theory is a topic that comes up fairly regularly in competitive programming, and it’s a very nice fit for Haskell. I’ve developed a bunch of code over the years that regularly comes in handy. None of this is particularly … Continue reading

## Anafunctors

This is part four in a series of posts on avoiding the axiom of choice (part one, part two, part three). In my previous post, we considered the “Axiom of Protoequivalence”—that is, the statement that every fully faithful, essentially surjective … Continue reading

Posted in category theory, math, species
Tagged AC, anafunctor, axiom of choice, category, constructive, equivalence, functor, isomorphism, theory, types, unique
5 Comments

## AC and equivalence of categories

This is part three in a series of posts on avoiding the axiom of choice (part one, part two). In my previous post, I explained one place where the axiom of choice often shows up in category theory, namely, when … Continue reading

Posted in category theory, math, species
Tagged AC, axiom of choice, category, constructive, equivalence, functor, isomorphism, theory, types, unique
5 Comments

## Unique isomorphism and generalized “the”

This is part two in a series of posts on avoiding the axiom of choice; you can read part one here. In category theory, one is typically interested in specifying objects only up to unique isomorphism. In fact, definitions which … Continue reading

Posted in category theory, math, species
Tagged AC, axiom of choice, category, constructive, functor, isomorphism, theory, types, unique
8 Comments