@@ -288,3 +288,9 @@ fmap g (fmap f x) = liftA1 g (liftA1 f x)
288288 = liftA1 (g . f) x
289289 = fmap (g . f) x
290290```
291+
292+# Sources
293+
294+[https://wiki.haskell.org/Typeclassopedia](Typeclassopedia) contains a thorough
295+description of the most ubiquitous typeclasses together with explanation of
296+their laws and with more exercises.