i assume is a cardinal number such that . otherwise, it is not true

we can prove the claim by showing:

(1) and (2)

(1) is immediate.

for (2): ....there should be a theorem in your book telling you something to that effect

hint: is the cardinal number of by definition. you can prove that this cardinal number is also infinitely countable, which will show that it is equal to . the way i usually see this done is by the use of a diagram, you should also see a proof using this technique in your text. the diagram looks like a grid, with the elements of along the first row and column, and the elements in the inner cells are there corresponding products. you count off the elements in diagonals ...or

Xo * Xo = Xo

Help anyone?