The supply will reduce because of bitcoin halving and the demand will increase because of people that will buy because of anticipation.
wrong, the bitcoin supply is constantly rising at all times as new blocks are found. this won't change after halving. the only thing that changes (halves) is the amount of new coins that can be created. so you can say the supply creation rate is reduced not the supply itself.
also demand doesn't magically increase even if supply decreased!