Instance of |CoreProperties| holding the read/write Dublin Core
        document properties for this presentation. Creates a default core
        properties part if one is not present (not common).

def core_properties(self):
        """
        Instance of |CoreProperties| holding the read/write Dublin Core
        document properties for this presentation. Creates a default core
        properties part if one is not present (not common).
        """
        try:
            return self.part_related_by(RT.CORE_PROPERTIES)
        except KeyError:
            core_props = CorePropertiesPart.default()
            self.relate_to(core_props, RT.CORE_PROPERTIES)
            return core_props