Unfortunately, if Ψ + Γ is the set of all consequences of Γ which can be built this way, there is in general no finite subset Ψ Γ of Ψ + Γ such that Ψ Γ |= ψ for all ψ ∈ Ψ + Γ .
the complex classes to be used must be selected, which is not trivial.