Book: The Little Schemer, by Friedman, D.

This book is focused on the Scheme programming language, and follows an interesting writing style, where questions are asked on the left panel and answered on the right. It is akin to how a children would learn a new skill, by trial an error and with an explanation of the solution.

With the book there are also certain laws and commandments that are given as a ground truth for reference when coding.

Laws

All strings including symbols, numbers and special characters other than ( or ) are atoms.
All atoms, lists are S-expr.
Law of car: car is defined only on non-empty lists.
Law of cdr: cdr is defined only on non-empty lists. cdr returns another list.
Law of cons: cons take two arguments, the second being a list. The result is a list.
Law of null?: null? is only defined for lists.
Law of eq?: eq? takes two atoms (non numeric?).

Commandments

First commandment: Always ask null? as first question when recurring a list of atoms. When recurring on a number ask zero? as the first question.
Second commandment: Use cons to build lists.
Third commandment: When building a list, describe the typical element and then cons it onto the natural recursion.
Fourth commandment: Always change at least one argument when recurring. It must be changed to be closer to termination. The changing argument must be tested in the termination condition.
Fifth commandment: When building value with + (sum), use 0 for value of terminating condition. When building with x (multipy), always use 1 for the value of the terminating condition. With const, use '() as the value of the terminating condition.