Infinitism

Since infinity isn't a defined whole number, the problem infinity minus infinity could never be determined. Therefore, the answer is undefined.

Infinity is not an exact number it is an idea that implies that the number is very very very very very very large number, or also expresses arbitarily growth in function. Because infinty is not an exact number therefore operations on infinity is not defined.

Consider an infinite number of boxes to supply an infinite number of objects. If we try to subtract infinite number of boxes used from that we have, we can't tell if we have enough or not.

We have that infinite is an infinite amount of numbers, but no only positive number and integers, also we have fractions, decimal, positive, negative numbers, etc. Negative infinite is the same than a positive infinite, by that we cans say that Infinite - Infinite = Undefined

Formally, $a - a = 0$ in most situation, but if $a = \infty$ , then it is undefined.

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Any numbers are added to the number, $\infty$ , it is always $\infty$ although the adding number is positive infinity or negative infinity.