(6) a. Mary-ka Chelswu-∅ manna-ss-e. Mary-Nom Chelswu meet-Past-Dec 'Mary met Chelswu.'
in this case, a speaker uses ka-marked nominal X in order to convey the following meaning: the meaning of 'X (and only X) ...' or 'it is X that ...' the nominal with -ka is generally a discourse-new information.