consider o, m being set ;
take 1Cat (o,m) ; :: thesis: 1Cat (o,m) is discrete
let f be Morphism of (1Cat (o,m)); :: according to NATTRA_1:def 19 :: thesis: ex a being Object of (1Cat (o,m)) st f = id a
consider a being Object of (1Cat (o,m));
take a ; :: thesis: f = id a
thus f = m by TARSKI:def 1
.= id a by TARSKI:def 1 ; :: thesis: verum