In logic, the symbol ⊨, ⊧ or is called the double turnstile. It is often read as "entails", "models", "is a semantic consequence of" or "is stronger than".[1] It is closely related to the turnstile symbol , which has a single bar across the middle, and which denotes syntactic consequence (in contrast to semantic).
The double turnstile is a binary relation. It has several different meanings in different contexts:
In TeX, the turnstile symbols ⊨ and are obtained from the commands \vDash
and \models
respectively.
In Unicode it is encoded at U+22A8 ⊨ TRUE (⊨, ⊨) , and the opposite of it is U+22AD ⊭ NOT TRUE (⊭) .
In LaTeX there is the turnstile package, which issues this sign in many ways, including the double turnstile, and is capable of putting labels below or above it, in the correct places. The article A Tool for Logicians is a tutorial on using this package.