reserve a,x,y for object, A,B for set,
  l,m,n for Nat;

theorem Th18:
 for x being object holds  <*x*> in A* iff x in A
proof let x be object;
  rng <*x*> = {x} by FINSEQ_1:38;
  then {x} c= A iff <*x*> is FinSequence of A by FINSEQ_1:def 4;
  hence thesis by FINSEQ_1:def 11,ZFMISC_1:31;
end;
