Here is an example. Let us consider

Here is an example. Let us consider the following structure Σ : with + for addition, × for multiplication, s for function, successor,  for even number, and  for primary number, and the open sentence F: “if x is an even number, then its successor is a primary number.” 4 satisfies F ; indeed 4 is even, and 5 is primary ; 8 doesn’t satisfy F, for 8 is even, and 9 is not primary ; notice that, although this might not be obvious for most of us, every odd number satisfies F ; indeed, the antecedent of the conditional is false^5