Re: Second-order and Higher-order Logic

Herman Jurjus schrieb:
Aatu Koskensilta wrote:
Henkin semantics

This reminds me:
Does anyone know if it's possible to prove [some form of] independence of CH in a 3rd order system (with 3 sorts, mimicking : N, P(N) and P(P(N)) ?

No, probably ZFC and 3rd order arithmetic is not enough.
You need some forcing notion definitions as well.
.

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