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MIT OpenCourseWare (OCW) offers free, openly accessible course materials from MIT. You can browse courses across engineering, science, and humanities to access syllabi, lecture notes, assignments, exams, and, where available, video lectures for self-paced study.
More resources on Categories
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Kerodon
Higher category theory reference by Riehl and Lurie
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Category Theory for Programmers
Companion site to Milewski's videos with free book
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nLab
Comprehensive wiki on category theory
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Category Theory Introduction
Paolo Perrini beginner video
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Category Theory for Programmers: Part 1
Bartosz Milewski introduces categories
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Lectures on Category Theory
Learn category theory from Tom Leinster's lectures! This course explores categories, functors, and natural transformations.