Turnstile (Symbol)

In mathematical logic and computer science, the turnstile is the symbol written as a vertical bar joined to a horizontal bar, named for its resemblance to a physical turnstile gate. It is also called tee and is commonly read aloud as yields, proves, satisfies or entails. The symbol denotes a binary relation between a set of premises and a conclusion, and its precise meaning shifts with context: in proof theory it typically expresses syntactic derivability, that a formula can be derived from a set of assumptions using the rules of a formal system, while a related double-turnstile symbol is used elsewhere for semantic entailment.