Editing Unification (computer science) (section)

===Application: unification in logic programming===
The concept of unification is one of the main ideas behind [[logic programming]]. Specifically, unification is a basic building block of [[Resolution (logic)|resolution]], a rule of inference for determining formula satisfiability. In [[Prolog]], the equality symbol <code>=</code> implies first-order syntactic unification. It represents the mechanism of binding the contents of variables and can be viewed as a kind of one-time assignment.

In Prolog:
# A [[variable (programming)|variable]] can be unified with a constant, a term, or another variable, thus effectively becoming its alias. In many modern Prolog dialects and in [[first-order logic]], a variable cannot be unified with a term that contains it; this is the so-called ''[[occurs check]]''.
# Two constants can be unified only if they are identical.
# Similarly, a term can be unified with another term if the top function symbols and [[arities]] of the terms are identical and if the parameters can be unified simultaneously. Note that this is a recursive behavior.
# Most operations, including <code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>, are not evaluated by <code>=</code>. So for example <code>1+2 = 3</code> is not satisfiable because they are syntactically different. The use of integer arithmetic constraints <code>#=</code> introduces a form of E-unification for which these operations are interpreted and evaluated.<ref>{{cite web |title=Declarative integer arithmetic |url=https://www.swi-prolog.org/pldoc/man?section=clpfd-integer-arith |website=SWI-Prolog |access-date=18 February 2024}}</ref>