Re: [isabelle] Full vs Henkin Semantics

Hi Andrew,

>> Is HOL in Isabelle/HOL based on full semantics or Henkin semantics [1]?

I would say that the HOL-based provers, including Isabelle/HOL, can be seen as "based on Henkin semantics" because of what Larry pointed out: 
that HOL deduction is sound and complete w.r.t. (a proper notion of) Henkin semantics. The deduction is of course sound for the full-frame semantics. 

Another note: As far as I see, what the theorem proving community calls "the HOL logic" is something quite specific, introduced in Mike Gordon's seminal HOL system: classic higher order logic with infinity, choice, rank-1 polymorphism, constant definitions and a "typedef" mechanism for introducing new types by carving out non-empty subsets of existing types. Isabelle/HOL additionally includes overloaded  constant definitions (with possible delay and recursion in the overloading process), which form the basis of type classes.  A proper notion of Henkin semantics needs to account for all these.  



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