# Predicate symbol

(Redirected from Relation symbol)

predicate letter

A notation for some concrete predicate or relation. E.g., the symbol $\leq$ often denotes the order relation on the real numbers; it is a $2$-place predicate. In the formal structure of a language, the symbols denoting predicates must be used, in a well-defined way, for constructing expressions of the language. In particular, if $P$ is an $n$-place (or $n$-ary) predicate symbol, then the following rule should be among the syntactic rules for forming expressions in the formalized language: "If $t_1,\ldots,t_n$ are terms, then $P(t_1,\ldots,t_n)$ is a formula". Thus, predicate symbols are syntactically used to form formulas, and semantically denote predicates.

#### References

 [1] S.C. Kleene, "Introduction to metamathematics" , North-Holland (1951) [2] Yu.L. Ershov, E.A. Palyutin, "Mathematical logic" , Moscow (1970) (In Russian)