“A Greek myth is a set of multiforms or variants in the
same story, which exist either as written texts, prose or verse, or in oral
form, or in both written and oral form, or in vase paintingor plastic art as
well or independently. The story concerns the divine or the supernatural or the
heroic or animals or paradigmatic humans living in a time undefinable by human
chronology. Each retelling or application produces a new variant, which stands
in some degree of antagonistic relation to other variants or other myths and
thus takes its place in a system constituted by the proliferation of such
relations. This definition can incorporate the now current definition of myth
as ‘traditional tale,’ provided that the difficult word ‘traditional’ means
‘without an identifiable author.’ A variant can thus be more precisely defined
as the encounter of traditional tale and unique, individual, motivated
retelling or artistic reuse of that tale.” p. 15

Edmunds, Lowell, ed.,  Approaches
to Greek Myth
, Johns Hopkins, 1989.