Turnstile (symbol)

In mathematical logic and computer science the symbol ${\displaystyle \vdash }$ has taken the name turnstile because of its resemblance to a typical turnstile if viewed from above. It is also referred to as tee and is often read as "yields", "proves", "satisfies" or "entails". The symbol was first used by Gottlob Frege in his 1879 book on logic, Begriffsschrift.

Per Martin-Löf (1996) analyzes the ${\displaystyle \vdash }$ symbol thus: "...[T]he combination of Frege's Urteilsstrich, judgement stroke [ | ], and Inhaltsstrich, content stroke [—], came to be called the assertion sign." Frege's notation for a judgement of some content ${\displaystyle A}$

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