Ha Ha, the Thread Says "Not just sets of ordered pairs",
But Dan-O-Matic nevertheless rants:
> Since the addition function is not defined in the ZFC
axioms, you would first have to prove its existence
using only the ZFC axioms
If I remember well you use pairs resp. triples for your proof
of existence of addition? But why is then your addition
not just set, since you proved it like that?
The answer is the "Working Practice" uses different cosmetics.
This is what causes Dan-O-Matik a sisyphus. He invented the
Function Axiom, because he does not want to write (x,y) e f,
he prefers that from the outside one sees f(x,y).
The problem is that his Function Axiom transfers a set-like
function into a FOL function symbol. But FOL function symbols
are classes and not sets. But the Function Axiom is
totally unnecessary, I can directly prove:
1. โx (x, n, x) โ a โง โx โy โz ((x, y, z) โ a โ (x, i(y), i(z)) โ a) โ (i(i(n)), i(n), i(i(i(n)))) โ a
2. (i(i(n)), i(n), i(i(i(n)))) โ a (Tโ2 1)
3. ยฌ(โx (x, n, x) โ a โง โx โy โz ((x, y, z) โ a โ (x, i(y), i(z)) โ a)) (Tโ1 1)
4. ยฌโx โy โz ((x, y, z) โ a โ (x, i(y), i(z)) โ a) (Fโง2 3)
5. ยฌโx (x, n, x) โ a (Fโง1 3)
6. ยฌ(i(i(n)), n, i(i(n))) โ a (Fโ 5)
7. ยฌโy โz ((i(i(n)), y, z) โ a โ (i(i(n)), i(y), i(z)) โ a) (Fโ 4)
8. ยฌโz ((i(i(n)), n, z) โ a โ (i(i(n)), i(n), i(z)) โ a) (Fโ 7)
9. ยฌ((i(i(n)), n, i(i(n))) โ a โ (i(i(n)), i(n), i(i(i(n)))) โ a) (Fโ 8)
10. (i(i(n)), n, i(i(n))) โ a (Fโ1 9)
โ (ax 6, 10)
10. ยฌ(i(i(n)), i(n), i(i(i(n)))) โ a (Fโ2 9)
โ (ax 10, 2)
You can further restrict a and show that it exists. But
its NOWHERE NEEDED TO PROVE 2+1=3. You only
more about a when you for example want to prove:
2+1 =\= 4
But it would be more easier to abandon the Function Axiom
and provide some notation based on Peano Apostroph, or
some such. And not run into class problems and
function spaces that are as big as the universal class.