Mar 14:19. Εἷς καθεῖς) So Joh 8:9, and ὁ δὲ καθεῖς; Rom 12:5.-ὁ καθεὶς δὲ τὼν φίλων; 3Ma 5:31. From κατὰ (not καὶ εἶτα) and εἷς comes καθεὶς, of similar formation to ὀυδεὶς, μηδεὶς, unless you prefer accenting it καθεῖς, in order to distinguish it from the participle καθεὶς; κατὰ is used adverbially, as ἀνὰ μετά.