Freemans article can be found here : Freeman’s article on Birds and Frogs

What is the difference between how a bird and a frog approach mathematics? Are there any textbooks or books in which the author clearly has a froggy or birdlike approach to the subject? How does this compare in a course of pure mathematics? For example a course in real analysis as taught in a froglike way v.s a birdlike way; with such a rigorous course how can you approach this as a frog (problem solver)? It would be nice to see some simple and concrete examples and if you can recommend some textbooks on math subjects which teach both styles of mathematics. I am trying to find authors (mathematicians) who have written math textbooks, recreational math books, pure math books or problem solving books in their style. I want to see the advantages and disadvantages of both for my own personal learning and for teaching to students.