"Iff" is not expressible in independence-friendly logic
arXiv:0806.4785
Abstract
Ordinary first-order logic has the property that two formulas ϕand ψhave the same meaning in a structure if and only if the formula ``ϕiff ψ'' is true in the structure. We prove that independence-friendly logic does not have this property.
18 pages. Submitted to the Journal of Symbolic Logic