Does 1,9999...=2?

What about 0,4999...=0,5 or 0,00...(infinite zeroes)...1 = 0?

Yes, mathematics is THE most rigorously defined science in existence. Bertrand Russell's "Principia Mathematica" takes over 360 pages to get to one of the lemmas that will be used to show 1+1=2.

See http://upload.wikimedia.org/wikipedia/en/4/48/PM1%2B1%3D2lemma.jpg