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User:Michiexile/MATH198/Lecture 4

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IMPORTANT NOTE: THESE NOTES ARE STILL UNDER DEVELOPMENT. PLEASE WAIT UNTIL AFTER THE LECTURE WITH HANDING ANYTHING IN, OR TREATING THE NOTES AS READY TO READ.
IMPORTANT NOTE: THESE NOTES ARE STILL UNDER DEVELOPMENT. PLEASE WAIT UNTIL AFTER THE LECTURE WITH HANDING ANYTHING IN, OR TREATING THE NOTES AS READY TO READ.
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===Product===
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* Cartesian product in Set
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* Product of categories construction
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* Record types
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* Categorical formulation
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** Universal X such that Y
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===Coproduct===
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* Diagram definition
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* Disjoint union in Set
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* Coproduct of categories construction
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* Union types
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===Limits and colimits===
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* Generalizing these constructions
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* Diagram and universal object mapping to (from) the diagram
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* Express product/coproduct as limit/colimit
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* Issues with Haskell
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** No dependent types
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** No compiler-enforced equational conditions
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** Can be ''simulated'' but not enforced, e.g. using QuickCheck.
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====Useful limits and colimits====
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=====Equalizer, coequalizer=====
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* Kernels, cokernels, images, coimages
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** connect to linear algebra: null spaces et.c.
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=====Pushout and pullback squares=====
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* Computer science applications
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* The power of dualization.
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* Limits, colimits.
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* Products, coproducts.
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* Equalizers, coequalizers.

Revision as of 16:13, 7 October 2009

IMPORTANT NOTE: THESE NOTES ARE STILL UNDER DEVELOPMENT. PLEASE WAIT UNTIL AFTER THE LECTURE WITH HANDING ANYTHING IN, OR TREATING THE NOTES AS READY TO READ.

Contents

1 Product

  • Cartesian product in Set
  • Product of categories construction
  • Record types
  • Categorical formulation
    • Universal X such that Y

2 Coproduct

  • Diagram definition
  • Disjoint union in Set
  • Coproduct of categories construction
  • Union types

3 Limits and colimits

  • Generalizing these constructions
  • Diagram and universal object mapping to (from) the diagram
  • Express product/coproduct as limit/colimit
  • Issues with Haskell
    • No dependent types
    • No compiler-enforced equational conditions
    • Can be simulated but not enforced, e.g. using QuickCheck.

3.1 Useful limits and colimits

3.1.1 Equalizer, coequalizer
  • Kernels, cokernels, images, coimages
    • connect to linear algebra: null spaces et.c.
3.1.2 Pushout and pullback squares
  • Computer science applications 
   * The power of dualization.
   * Limits, colimits.
   * Products, coproducts.
   * Equalizers, coequalizers.
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