@viole,
This is the *actual* definition of a subset.
A(x) ⊆ B(y) if ∀A(x):{x ∈ A(x) → x ∈ B(y)}
That's it. It's a defintion.
"→" means "~{x ∈ A(x)}" is completely irrelevant, because "→" is defined that way.
But "→" does not describe the relationship between unknown Jews and their atheism/theism.
"→" means "suppose" or "assume it's true"
If Jews are unknown, there is NO reason to suppose or assume anything.
And that's why this fails. There might be occasion when it makes sense to assume it's true unless it's proven false. This isn't one of them.
But the point is:
"A(x) ⊆ B(y) if ∀A(x):{x ∈ A(x) → x ∈ B(y)}"
IS NOT:
"Suppose A and B are sets. If every element of A is also an element of B, then we say A is a subset of B, and we denote this as A ⊆ B. We write A ⊈ B if A is not a subset of B, that is, if it is not true that every element of A is also an element of B. Thus A ⊈ B means that there is at least one element of A that is not an element of B."
It is *actually* this:
Suppose A and B are sets, and assuming that it's true that every element of A is also an element of B, then we say A is a subset of B, and we denote this as A ⊆ B. We write A ⊈ B if A is not a subset of B, that is, if it is proven that an element of A is not an element of B. Thus A ⊈ B means that there is at least one element of A that is not an element of B.
See the difference?
This is detailed in the PDF after chapter 1 under conditional statements. In that section, it makes the comparrison where the assumption is: "Assuming you pass the final exam, you will pass the course." But, they say, if you don't pass the exam, the teacher might choose to pass you anyway. They could make that executive decision to bypass the defintion of the final exam.
But in this case, you cannot make the executive decision to change the meaning of Jew, Atheist, and Theist, such that a Jew can be both Athiest and Theist simultaeously. That's why my proof works, and it works for any set, any property, any proposition, excluding its indentity.
Anyway, you need to advance past chapter 1. Advancing past chapter 1, changes the definition of a subset into an "assume it's always true" defintion. But belief in a god or gods, is NOT an assume it's always true definition.
Okie, dokie?