  An open market is a subset of an entire equity market composed of a certain
fixed number of top capitalization stocks. Though the number of stocks in the
open market is fixed, the constituents of the market change over time as each
company's rank by its market capitalization fluctuates. When one is allowed to
invest also in the money market, the open market resembles the entire 'closed'
equity market in the sense that the equivalence of market viability (lack of
arbitrage) and the existence of numeraire portfolio (portfolio which cannot be
outperformed) holds. When access to the money market is prohibited, some topics
such as Capital Asset Pricing Model (CAPM), construction of functionally
generated portfolios, and the concept of the universal portfolio are presented
in the open market setting.
