  The lexicographic closure of any given finite set D of normal defaults is
defined. A conditional assertion "if a then b" is in this lexicographic closure
if, given the defaults D and the fact a, one would conclude b. The
lexicographic closure is essentially a rational extension of D, and of its
rational closure, defined in a previous paper. It provides a logic of normal
defaults that is different from the one proposed by R. Reiter and that is rich
enough not to require the consideration of non-normal defaults. A large number
of examples are provided to show that the lexicographic closure corresponds to
the basic intuitions behind Reiter's logic of defaults.
