question: Find the names of schools that have some students playing in goalie and mid positions.
#1 return schools 
#2 return students of  #1 
#3 return positions of  #2 
#4 return #1 where  #3 is  goalie 
#5 return #1 where  #3 is  mid 
#6 return #1 of  both #4 and #5 
#7 return names of  #6