consider t being Element of T;
reconsider S = {t} as AntiChain_of_Prefixes by Th70;
take S ; :: thesis: S c= T
let x be set ; :: according to TARSKI:def 3 :: thesis: ( not x in S or x in T )
assume A1: x in S ; :: thesis: x in T
A2: x = t by A1, TARSKI:def 1;
thus x in T by A2; :: thesis: verum