Please help me with this question. I would really appreciate it.

student takes ID course id sec id semester ID name dept name tot_cred grade section course course id title dept name credits department dept name building budget advisor sec i0 semester ear building room_no time slot id time slot time slot day start time end_time prere instructor classroonm ID name dept name salary room n0 capacity teaches ID course id sec id semester ear Figure 2.8 Schema diagram for the university database. List all of the names of all instructors who were once students at the university Note: you will need to assume in order to write this query. State your assumption Express your answers in relational algebra. Your queries should NOT include unneeded relations