let t be Subset of (QuasiAdjs C); :: thesis: ex f being valuation of C st t at f c= t
take f = the empty valuation of C; :: thesis: t at f c= t
let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in t at f or x in t )
assume x in t at f ; :: thesis: x in t
then ex a being quasi-adjective of C st
( x = a at f & a in t ) ;
hence x in t by ABCMIZ_1:139; :: thesis: verum