reserve a,x,y for object, A,B for set,
  l,m,n for Nat;
reserve X,Y for set, x for object,
  p,q for Function-yielding FinSequence,
  f,g,h for Function;

theorem Th39:
  apply({},x) = <*x*>
proof
  len apply({},x) = 0+1 & apply({},x).1 = x by Def4,CARD_1:27;
  hence thesis by FINSEQ_1:40;
end;
