Having not really looked at Greek until just recently, I had seen no problem with English "four" and "five" being related to Latin "quattuor" and "quinque" through something as simple as Grimm's Law (k > x (h) > f (I had assumed this wasn't impossible, h and f being similar sounds)), but now I see that the Greek is "tetra" and "penta"... So what were the original consonants, and how did "t" and "p" happen? There seems to be a lot of that in Greek... Also, simpler questions: why (how) do some letters just disappear, as in *?TWR > feower (missing t), and why is there an m in "mono" (cf. one, unus, etc.)?