FOREX: discrepencies in exchange rates?

[Jim14Qc]

I've been wondering about this for a while and I'm 99% sure this is not a bug that exists, but anyway..

Are there funds that use computers to find discrepencies between currency prices (for example, currency A trading for 2 units of B, and B trading for 2 units of C, but A trading only for 3 units of C so you could get a huge return by using A to buy B to buy C to buy back more A)? If so, wouldn't these funds be a 100%-lock as far as profitability? Is that not possible because there is usually no discrepency even between currencies that have lesser volumes of trade?

Thansk.