I see the word "prepone" used a lot. Checked
http://www.m-w.com
never found a reference to the word. I found some sources on google quoting to be added to dictionary, 1998 Oxford to be precise. I havent gotten around checking the authencity/justification by looking at 1998 Oxford Dictionary
Until I find legitamate source justifying so it will remain a errored word I guess. However surfing for proofs, I hit this wonderful website which talks about mistakes people make in English. Please Enjoy /educate yourself.
http://www.wsu.edu/~brians/errors/errors.html#errors
http://en.wikipedia.org/wiki/Etymology
Disclaimer: I claim no authencity to the information on the above Website
