Open core and quasi-equilibria with lower semi-continuous preferences

This note introduces a new concept of core - open core, using which it show s a quasi-equilibrium existence result in an economy where consumers' prefe rence relations are assumed to be lower semi-continuous, but not necessaril y to have open lower sections nor to be open valued, such as the lexicograp hic ordering. As an application, a competitive equilibrium existence result without non-satiation assumption is proved. JEL Classification Number: D51 .