A First-order language in Zermelo-Fraenkel set theory consists of the following symbols:
- A set of constants, such as A, B, C, ...
- A set of n-ary relations such as >(x, y).
- A set of n-ary functions such as +(x, y).
- An infinite set of variables such as x, y, z,...
- The connectives , .
- quantifiers: , .
- parenthesis: , .
- The equality symbol .