Mathematics 6170: Category Theory
Instructor: Jonathan Smith.
email: jdhsmithATiastateDOTedu (substitute punctuation)
Office Hours: M 9:55 am, 11 am; F 9:55 am, 11 am (subject to change).
Grading: based on five graded homework assignments (final due Fri., 12/6).
Accessibility statement;
Free expression statement.
Class absence memo.
Textbook: S. Mac Lane, Categories for the Working Mathematician, 2nd. ed., Springer, ISBN 0387984038
The books by AdámekHerrlichStrecker (4MB) and Emily Riehl (1.5MB) are also available online.
Study Plan: reserve 1  2 hours for homework between each pair of classes. Successful performance in the class depends critically on completion of the homework assignments.
Communication devices must remain switched off during the class periods.
Syllabus: Basic constructions and terminology of category theory,
including limits, functors, natural transformations, adjoints,
cartesianclosed and enriched categories.
Assignments
10/14 for 10/16: Read Mac Lane, pp.889 "Duality functors ..." and p.93 "... skeleton ...".
Lesson summary
10/11 for 10/14: Read Mac Lane, Section IV.4.
Lesson summary
Third graded homework due 10/11:
Three questions from the following list of five: Section III.5: 5; Section III.6: 4; Section IV.2: 4, 5, 12.
10/9 for 10/11: Read Mac Lane, Section IV.3 and Riehl, Definition 4.5.12 through Example 4.5.14(v).
Lesson summary
10/7 for 10/9: Read Mac Lane, Section III.2 and Riehl, Section 2.2.
Lesson summary
10/4 for 10/7: Read Mac Lane, Section II.6.
Lesson summary
10/2 for 10/4: Read Mac Lane, Section IV.5.
Lesson summary
9/30 for 10/2: Read Mac Lane, Section IV.2.
Lesson summary
9/27 for 9/30: Read Mac Lane, Section IV.1, first six pages. Do IV.1, Exercise 3.
Lesson summary
Second graded homework due 9/27:
Three questions from the following list of five: Section I.4: 3, 5; Section III.4: 4, 5, 8.
9/25 for 9/27: Read Mac Lane, Section III.6 (just "only if" direction of Proposition 1).
Lesson summary
Consider a group G in the category Set, as defined on p.75 of Mac Lane.
Show that G need not be a group.
9/23 for 9/25: Read Mac Lane, Section III.5.
Lesson summary
9/20 for 9/23: Read Mac Lane, Section II.3 and Riehl, Definition 1.3.11 through Definition 1.3.13.
Lesson summary
9/18 for 9/20: Complete reading of Mac Lane, Sections III.3, 4.
Lesson summary
9/16 for 9/18: Read Mac Lane, Section III.4 from Infinite products through Pullbacks and Section III.3 from Infinite Coproducts through Cokernel Pair. Do Exercise III.4.9.
Lesson summary
9/13 for 9/16: Read Mac Lane, Section III.4 Products and Section III.3 Coproducts.
Lesson summary
Suppose that the product of objects X and Y exists in a category.
Show that it is isomorphic to the product of Y and X.
9/11 for 9/13: Read Mac Lane, Section II.4 and Riehl, Definition 3.1.1.
Lesson summary
Do Mac Lane, Exercise II.4.3, and interpret the polynomial ring R[X] as a graded abelian group.
9/9 for 9/11: Read Mac Lane, Sections II.12.
Lesson summary

Give an example of a monoid M that is not isomorphic to its opposite M^{op}.

Prove that there is no monoid isomorphism between M and M^{op}.
First graded homework due 9/9:
Three questions from the following list of five: Section I.3: 2, 4; Section I.5: 2, 6, 7.
9/6 for 9/9: Read Mac Lane, Section I.4.
Lesson summary
9/4 for 9/6: Read Mac Lane, Section I.3.
Lesson summary
8/30 for 9/4: Read Mac Lane, Section I.5.
Lesson summary

Prove the lemma in the lesson summary.

Show that any two terminal objects are isomorphic.

Show that the inverse of an invertible morphism is unique.

Give an example of a monomorphism in Set which is not split.
8/28 for 8/30: Read Mac Lane, Sections I.1, I.2.
Lesson summary

Consider the function sending each object of a category to the identity function at that object. Show that the function is injective.

Show that the identity morphism at an object of a category is uniquely determined by Mac Lane's condition (2) on page 8.
8/26 for 8/28: Give an example of a directed graph C that is not isomorphic to its dual C^{op}. Prove that there is no directed graph isomorphism between C and C^{op}.
Lesson summary