So, let’s have a look again, and let’s take tis look from a “game theory” point of view in the sense that there exist different strategies:
(but first some words about infinity that already have been mentioned here:
there are as many natural numbers, as there are even or odd numbers (even though even plus odd makes up the naturals). There are as many integer numbers as there are natural numbers, even though the naturals are “only” the positive branch of the integers. There are as many fractions (rational numbers) as there are naturals. This all comes from Cantor’s diagonal argument. These sets are called “countable infinite” sets, because you can map them one-on-one onto the natural numbers which you could count (if you have infinite time that is). The “real numbers”, which are the rationals plus irrationals (like Pi, e, 2^(1/2) which cannot be expressed by fractions), cannot be mapped in such a way. This is an “uncountable infinite” set, and there are more reell numbers than naturals.)
So, let’s look at our two players (A and B) and different strategies (for simplicity i assume both A and B be male)
(1) A gives B ascending numbers (starting with one, not giving back a number that B already had), B gives A his lowest number:
So, it will look like that:
A -> B: 1,2
B -> A: 1
A -> B: 3,4
B -> A: 2
etc.
B will give back all numbers back to A, having an empty bag at the end (2*“amount of naturals”=“amount of naturals”!), A will have all numbers.
(2)A gives B his lowest numbers (inlcuding those given beforeand handed back), B gives A his highest number.
A -> B: 1,2
B -> A: 2
A -> B: 2,3
B -> A: 3
etc.
So, A will have given all numbers to B, and end up with an empty bag, while B has all natural numbers.
(3)A gives B his lowest numbers (inlcuding those given beforeand handed back), B gives A his lowest number.
A -> B: 1,2
B -> A: 1
A -> B: 1,3
B -> A: 1
etc.
So, A will have given all numbers to B, and end up with an empty bag except for the “1”, while B has all natural numbers, except for the “1”.
(4) A gives even numbers, B does anything:
A will have all odd numbers at least, regardless of B’s strategy. So, A has an infinite amount of numbers. The exact amount of B depends on what B does.
So, the answer:
you can’t tell, unless you know how they choose to give and give back numbers. It can be anything from nothing over any finite number (by changing strategies halfway) to an infinite amount.