[[Syntax]] | [[Terms]] | [[Equations]] | [[Horn formulas]] | [[Universal formulas]] | [[First-order formulas]] | [[Theories]]

A list of some first-order formulas.

|$R$ is a function  |$\forall x\exists y(xRy)\mbox{ and }\forall x,y,z(xRy\mbox{ and }xRz\Longrightarrow y=z)$  |
|$f$ is onto  |$\forall y\exists x(f(x)=y)$  |