The Wikipedia page on unit types is completely accurate with regards to what a unit type is, and a unit type is the correct model for the type that a void funct

The Wikipedia page on unit types is completely accurate with regards to what a unit type is, and a unit type is the correct model for the type that a void function returns in C. Sure, void can be interpreted in a few different ways, but void in function return or argument position definitely cannot be interpreted as the bottom type. As far as I know, C does not really have bottom as a first-class concept, however useful it might be. So while I agree with you that it would be theoretically possible for C's statement about void not having any inhabitants to coincide with the type theoretic defintion of void, in practice it does not (for all the reasons I mentioned earlier). You will note that all the differences mentioned between void and unit in the Wikipedia article are syntactic, not semantic; this is because semantically there is no real distinction between them. What is bizarre to me, though, is that you didn't read the Wikipedia article you just carelessly edited, which already mentions Common Lisp and explicitly tells you not to confuse the NULL type (which has single inhabitant NIL--i.e. you agree with me that it is the same as void, and they are both unit types) with the NIL type (bottom). Firstly, the existence of a subtyping relationship that lets you upcast values of type unit to values of type symbol (or indeed, any other type) does not somehow make it not a unit type (only subtyping in the other direction would accomplish such a thing), and certainly does not invalidate any of the article's claims as you assert. Secondly, no implementation detail of Common Lisp will affect the definition of a unit type, regardless of how many edits one makes to a Wikipedia page, any more than the C standard claiming void functions don't have a return type changes how they are modeled mathematically. Notions as fundamental as unit types are defined semantically and aren't really tied to specific language syntax.