Form a list twice as long as the longest of the arguments
callput, K, time whose
first half consists of AmericanOption objects and
second half consists of EuropeanOption objects
having the same exercise specification
control_variate_pairs(callput, K, time)1 for calls, -1 for puts
strike
Time from 0 until expiration
Other American Exercise Equity Options: 
american_implied_volatility(),
american()