You will need to first break up [Select 2] into its parts.
var text PartOne = Part([Select 2],1,";");
var text PartTwo= Part([Select 2],=2,";");
etc etc etc
var text PartTwenty = Part([Select 2],20,";");
var text StepOne =
List(";", [Select 1], IF(not Contains([Select 1], $PartOne), $PartOne);
var text StepTwo =
List(";", $StepOne, IF(not Contains($StepOne, $PartTwo), $PartTwo);
var text StepThree =
List(";", $StepTwo, IF(not Contains($StepTwo, $PartThree, $PartThree);
etc etc etc
var text StepTwenty =
List(";", $StepNineteen, IF(not Contains($StepNineteen, $PartTwenty, $PartTwenty);
$StepTwenty