final AmericanExercise ex = (AmericanExercise)a.exercise;
QL.require(!ex.payoffAtExpiry() , PAYOFF_AT_EXPIRY_NOT_HANDLED); // QA:[RG]::verified
QL.require(a.payoff instanceof StrikedTypePayoff , NON_STRIKE_PAYOFF_GIVEN); // QA:[RG]::verified
final StrikedTypePayoff payoff = (StrikedTypePayoff)a.payoff;
final double /*@Real*/ variance = process.blackVolatility().currentLink().blackVariance(ex.lastDate(), payoff.strike());
final double /*@DiscountFactor*/ dividendDiscount = process.dividendYield().currentLink().discount(ex.lastDate());
final double /*@DiscountFactor*/ riskFreeDiscount = process.riskFreeRate().currentLink().discount(ex.lastDate());
final double /*@Real*/ spot = process.stateVariable().currentLink().value();
QL.require(spot > 0.0, "negative or null underlying given"); // TODO: message
final double /*@Real*/ forwardPrice = spot * dividendDiscount / riskFreeDiscount;