function GetMainConjunction(const Expression: string): string;
var
  P: PChar;
  BraceCnt: Integer;
begin
  Result := '';
  BraceCnt := 0;
  P := PChar(Expression);

  while P^ <> #0 do
  begin
    case P^ of
      '(': Inc(BraceCnt);
      ')': Dec(BraceCnt);
    end;
    Inc(P);

    if BraceCnt = 0 then
    begin
      while (P^ = ' ') do
        Inc(P);
      SetString(Result, P, 2);
      Exit;
    end;
  end;
end;