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We solve the problem of approximating in ℒ 2 a given random variable H by stochastic integrals G T (ϑ) of a given discrete-time process X. We interpret H as a contingent claim to be paid out at time T, X as the price evolution of some risky asset in a financial market, and G(ϑ) as the cumulative gains from trade using the hedging strategy ϑ. As an application, we determine the variance-optimal strategy which minimizes the variance of the net loss H − G T (ϑ) over all strategies ϑ.
Martin Schweizer (Wed,) studied this question.