Discrete Mathematics using a Comptuter (O’Donnell, Hall, Page) Chapter 10
Discrete Mathematics with Applications - Metric Edition (Epp) Chapter 8
The Haskell Road to Logic, Math and Programming (Doets, van Eijck) 5
https://www.cs.carleton.edu/faculty/dln/book/ch08_relations_2021_September_08.pdf
https://www.cs.yale.edu/homes/aspnes/classes/202/notes.pdf Chapter 9
https://runestone.academy/ns/books/published/ads/chapter_7.html
https://runestone.academy/ns/books/published/ads/s-function-def-notation.html
https://runestone.academy/ns/books/published/ads/s-properties-of-functions.html
https://runestone.academy/ns/books/published/ads/s-function-composition.html
https://runestone.academy/ns/books/published/DiscreteMathText/chapter8.html
https://runestone.academy/ns/books/published/DiscreteMathText/relations8-1.html
https://runestone.academy/ns/books/published/DiscreteMathText/rstrelations8-2.html
https://runestone.academy/ns/books/published/DiscreteMathText/equivalencerelations8-3.html
https://runestone.academy/ns/books/published/DiscreteMathText/modarith8-4.html
https://en.wikipedia.org/wiki/Relation_(mathematics)