reserve X for set;
reserve UN for Universe;

theorem Th21:
  FinSETS is trivial & SETS is non trivial
  proof
    SETS is_Tarski-Class_of FinSETS by CLASSES1:def 4;
    then omega c= FinSETS in SETS & SETS is axiom_GU1 & SETS is axiom_GU3
      by Th16;
    hence thesis by Th13,Th19,Th20;
end;
