Logical expressions

thumb|The Pythagorean theorem has at least 370 known proofs.

formula that represents a mathematical object

logical formula which is true in every possible interpretation

mathematical notation in which every operator precedes all of its operands

logical quantification stating that a statement holds for all objects

mathematical logic concept

finite sequence of symbols from a given alphabet that is part of a formal language

type of logical formula in propositional logic

formula that contains at least one free variable

set of sentences in a formal language

expression in propositional calculus

In mathematical logic, a sequent is a very general kind of conditional assertion.

logical expression whose terms do not contain any variables

The T-schema ("truth schema", not to be confused with "Convention T") is used to check if an inductive definition of truth is valid, which lies at the heart of any realisation of Alfred Tarski's semantic theory of truth. Some authors refer to it as the "Equivalence Schema", a synonym introduced by Michael Dummett.

inference rule that may be applied to only a particular segment of an expression