function DeleteCopies(sentence:string): string;
var
    sequen: TSetChar;
    i, j: byte;
begin
    sequen := [];
    for i := 1 to length(sentence) do
        if not (sentence[i] in Sequen) then
            sequen := sequen + [sentence[i]];
    for i := 1 to length(sentence) do
        if  sentence[i] in sequen then
            ?????????????
    DeleteCopies := sentence;
end;