We start by defining a simple belief language and
model theory to be able to talk about the mental states of
various. We model beliefs using a modal operator BEL,
e.g. (BEL bill (have joe hammer)), with the usual
possible worlds semantics [Cohen & Levesque, 1990]. We
need to be able to talk about ‘pieces’ of information, which
in this present context refer syntactically to sentences, but
semantically are equivalent to constraints over possible
worlds, i.e. those worlds satisfying the expression. Goals,
however, refer to specific steps in plans in MALLET, to
which agents can make commitments.