The case for crumbling commodities - Citi Citigroup says that powerful performance in commodities over the last couple of years raises the plausibility that aggressive assumptions have further driven up prices that appear to be on the verge of correcting meaningfully; moreover, industries such as related resource extraction equipment and engineering services also face downward revaluation potential. Firm thinks the notion of unwinding "crowded trades" could make the decline sharper than probably is justified.