ncatlab.org
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nLab is a collaborative wiki-style knowledge base for higher category theory and related areas of mathematics, offering detailed definitions, explanations, and references for concepts like natural transformations, functors, and homotopy theory.
More resources on Natural Transformations
nLab: Natural Transformation
Comprehensive reference with definitions, examples, and references.
Natural Transformations - Category Theory
Clear explanation with vertical and horizontal composition.
Category Theory for Programmers
Learn natural transformations in Category Theory for Programmers with Bartosz Milewski's insightful video course. Master functional programming concepts!
mathworld.wolfram.com
MathWorld is Wolfram's extensive online mathematics encyclopedia, offering detailed articles on mathematical concepts, definitions, theorems, formulas, and worked examples with diagrams and cross-links. It covers a wide range of topics—from algebra and calculus to topology and category theory—providing explanations and references for further study.
ocw.mit.edu
MIT OpenCourseWare is a free, public repository of MIT course materials, offering lecture notes, assignments, exams, and sometimes video lectures from a wide range of courses. Users can browse by subject or department to study topics across science, engineering, math, humanities, and more.