I was expressing (4-0.99999...) as 3.000...0001
It is not correct to use "usual method" for computation in the infinite case.
Before computation, you have to give a precise meaning to symbols!
Infinity has been very controversial in the history of maths.
The fact is that a real number (that can be thought as a point in the line, measured respect a given unit segment" )has just one decimal representation, or two, but it can happen just in the cases similar to that one, for example
2,34 = 2,33999999999999.......

The only time I have seen this fact used was to prove that
"real numbers" are "more" than "integers numbers"
I know that it is hard to imagine that there are several steps of infinities... (infinite,indeed) and in fact it has been understood at the end of XIX century . The meaning - more or less - is that it is possible to imagine the integers numbers as a subset of the real numbers, but not viceversa.

I suppose that this post will start another discussion:
we would say that I am throwing a stone in the pond ( gettare un sasso nello stagno), in order to excite something quiet.