How can one prove that the Quraan has been unchanged for over 1400 years?

The simplest answer to this is the fact that:
1) The Holy Quran, unlike other books of religion, is only in Arabic
2) If you pick up a copy of the Quran from anywhere in the world, it will be exactly the same
3) It was preserved through memorization, thus a written form was not the only means of keeping it preserved