What is the ruling on reserving seats in lectures, and is it permissible to sit in a seat reserved for another person without their knowledge or consent, and what is the ruling on someone who did not approve of reserving seats, yet a reserved seat was found for them?

Whoever gets to something permissible first has a greater right to it. Therefore, it is not permissible to reserve seats in lecture halls for those who have not arrived at all. However, it is permissible for someone who was sitting and then got up for a reason to return to their seat, as they have a greater right to it than others. If one finds that another person has reserved a place, and one knows that someone else arrived there first and desires it, then that person has a greater right to it, and it is not permissible to sit there except with their consent. However, if there are other empty seats and it is highly probable that those who arrived earlier have no desire for that particular seat, then it appears there is no harm in sitting there. But if the seats are full and the earlier occupants cannot be identified, then it is not permissible to sit without their permission.