List of first-order theories
= List of first-order theories
{wiki=List_of_first-order_theories}
In mathematical logic, a first-order theory is a set of sentences (axioms) in first-order logic that describe a particular domain of discourse. Here are some well-known first-order theories: 1. **Peano Arithmetic (PA)**: This theory is used in number theory and consists of axioms that define the properties of natural numbers, including the principles of induction.