Sources/References

Yves Nievergelt. Foundations of Logic and Mathematics: Applications to Computer Science and Cryptography, Kindle Edition.

Manin, Y., & Koblitz, N. (2010). A course in mathematical logic for mathematicians (2nd ed.). New York: Springer.

Hurley, P. (2003). A Concise Introduction to Logic (8th ed.). Australia: Wadsworth/Thomson Learning.

Smith, D., & Eggen, M. (2011). A transition to advanced mathematics (7th ed.). Boston, MA: Brooks/Cole. 

We can obtain similar structures by altering our definition in various ways. Here  are some examples. 


John Harris. Combinatorics and Graph Theory (Undergraduate Texts in Mathematics) Springer. Kindle Edition.