replace MathSet by set, because mutable states not supported any more
replace MathSet by set, because mutable states not supported any more

necozay/tulip-control,necozay/tulip-control,necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control