By L, we denote the set of all propositional formulas. Let C be the set of
all clauses. Define C-0=C boolean OR {-L eta : eta is an element of }. In S
ec. 2 of this paper, we prove that for normal modal logics S; the notions o
f (S, C-0)-expansions and S-expansions coincide. In Sec. 3, we prove that i
f I consists of default clauses then the notions of S-expansions for I and
(S, C)-expansions for I coincide. To this end, we first show, in Sec. 3, th
at the notion of S- expansions for I is the same as that of (S, L)-expansio
ns for I.