Definition 22: A statement \phi is composite if we have one of the following:
(a) There are statements \psi and \xi such that \phi can be expressed as the conjunction (\psi \wedge \xi). (b) There is a statement \psi such that \phi can be expressed as the negation \neg \psi. (c) There is a statement \psi and a variable x such that \phi can be expressed as the existence statement \exists x \psi.