Is common symbol $\vdash$ an abuse of notation or there is a deep sacred connection between $$\Gamma \vdash \lambda(a:A).a:\Pi(a:A).A$$ which is preorder and $$G \vdash F \quad \mbox{($F$ is left adjoint to $G$)}$$ ?
(the source of misunderstanding is adjoined functor wiki)
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I found some useful here in Categorical Logic and Type Theory B.Jacobs (1999).
But I didn't understand about which categories author wrote.
The adjoint functor is not the normal turnstile, but the reverse turnstile ⊣
There is quite a strong relation between the adjoint functor and semantics, see "The Galois connection between syntax and semantics"
http://www.logicmatters.net/resources/pdfs/Galois.pdf
but that would make one expect the double turnstile to be used... It would be interesting to know if there is anything more to the use of this symbol.