he is a liar!
he said "all cretans are liars", meaning he is a liar...so he is lying about that.......meaning all cretans are truth tellers(or something of that sort), but that cant be true..because he just lied about all cretans being liars.....so the truth is a LIE!
But maybe when he lied about all cretans being liars...he was meaning not all of them are liars....so he is among that fraction of liars. there. he is the liar.
that brute !