 For further discussion of the kind of material presented in this section, see the SEP entries on:   set theory,  the early development of set theory, and  the axiom of choice. An excellent introduction to basic set theory is Enderton (1977); an informal but still rigorous introduction is Sheppard (2014); more advanced texts include Devlin (1993), Kunen (1983), and Jech (2006). For the higher reaches, to which we will come back in section  4, see Kanamori (2003).