How to prove that one of the numbers can be shown as subtraction of perfect squares?

[Ayylien64]

I'm stuck. I really don't know how to do this. Can you show me how to do this (at least show me the way to do it)?
I haven't done any progress because I don't understand this exercise.

The exercise:
Integer numbers a, b are positive numbers. Prove that at least one of the numbers a, b, a + b can be shown as subtraction of perfect squares of two integer numbers.

 

[stapel]

I'm stuck. I really don't know how to do this. Can you show me how to do this (at least show me the way to do it)?
I haven't done any progress because I don't understand this exercise.

The exercise:
Integer numbers a, b are positive numbers. Prove that at least one of the numbers a, b, a + b can be shown as subtraction of perfect squares of two integer numbers.

If either of a or b is odd, then the proof is easy. (here) The second reply here explains which of the evens can and cannot be expressed as a difference of squares.

So assume that each of a and b is of the form which cannot be expressed as a difference of perfect squares, and look at their sum. Where does this lead?