list1 - created by 3 appends: (DUS, ORD, SAN)
list2 - created by 3 insertFirsts: (JFK, DFW, LAX)
list1 after delete first: (ORD, SAN)
list1 after insert ZRH and BRU before SAN: (ORD, ZRH, BRU, SAN)
list3 - copy of list1: (ORD, ZRH, BRU, SAN)
list3 after clear: ()
list1 after list3 is cleared: (ORD, ZRH, BRU, SAN)
new list 3 - concatenated list1, list2: (ORD, ZRH, BRU, SAN, JFK, DFW, LAX)
list3 after reverse: (LAX, DFW, JFK, SAN, BRU, ZRH, ORD)
list1 after list3 reversed: (ORD, ZRH, BRU, SAN)
list2 after list3 reversed: (JFK, DFW, LAX)
should be an empty list: ()