1. Introduction
The creation and maintenance of a riskless hedge plays an essential role in
the derivation of the Black-Scholes option pricing formula. In the case of a
European call option, a hedge portfolio is constructed by establishing a long
position in the option and a short position in the underlying stock on which
the option is written. The relative position in the two securities in the hedge
portfolio is determined by the first partial derivative of the option pricing
formula with respect to the stock price. [For a more complete description, see
either Black and Scholes (1973) or Smith (1976).] Given their assumptions,
the effect of diffusion in the stock price is thus eliminated and with continual
adjustment of the hedge composition the value of the hedge at maturity
becomes riskless. Exploitation of this observation leads to the derivation of
the option pricing formulae.