barclays bank fined £26m for gold fixing, page-25

"What we have here is a documented case of actual market manipulation from which we can learn somethings:

1. To control the price of gold (create an artificial market) requires actual trades
2. The trader creating the artificial market usually has to pay a price.
3. Because of the expense, markets can only be controlled for relatively short periods of time."

I think you need to clarify our lesson as to which market are you talking about, and what period of time do you call short?

Evidently our teacher isnt talking about the London Gold Market, where according to Rosa Abrentes-Metz an authority on the subject of market manipulation and gold, the PM fix has shown clear signs of artificiality resulting from large downward movements (wink-wink) for over a decade:

http://www.bnn.ca/Video/player.aspx?vid=360038