In Category with Family by Castellan et al., they introduce the concept of Free SCWF as correspondence of STLC with base type. Seemingly, they define Free B-SCWF as the synonym of initial B-SCWF.

My question is, since this is a "free" scwf, I thought there should be free and forgetful functors between the category of B-SCWF and something. Where can I find (the citation of) such adjoint functors?

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    $\begingroup$ I would like to point out that, given any category $\mathcal C$ with initial object $0$, then the functor $F : \boldsymbol 1 \to \mathcal C$ mapping the one-object category to the initial object is the free functor, adjoint to $U : \mathcal C \to \boldsymbol1$. So in this sense the initial object is indeed free. $\endgroup$
    – Trebor
    Jun 8, 2022 at 4:16

1 Answer 1


The way to get a "free" functor rather than an initial object is to allow the $\mathcal B$ in the category $\mathcal B$-Scwfs to vary.

Then there is a forgetful functor $U$ from the category of Scwfs to the category of Sets that forgets everything except for the set of types. This has a left adjoint $F$, where $F(\mathcal B)$ is the Scwf defined in Proposition 4.

This is an instance of a general equivalence between left adjoints and collections of initial objects in certain slice categories, see the nlab for details.


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