the carrier of S in { the carrier of S} by TARSKI:def 1;
then [o, the carrier of S] in [: the carrier' of S,{ the carrier of S}:] by ZFMISC_1:87;
then [o, the carrier of S] in NonTerminals (DTConOSA X) by Th3;
hence [o, the carrier of S] is Symbol of (DTConOSA X) ; :: thesis: verum