# subroutine to merge two sorted lists

def merge (list1,list2):
    print (list1, list2)
    if len(list1) == 0 and len(list2) == 0:
        return []
    if len(list1) == 0:
        print("list 2",list2)
        return list2
    if len(list2) == 0:
        print("list 1",list1)
        return list1
    if list1[0] <= list2[0]:
        return [list1[0]] + merge(list1[1:], list2)
    if list2[0] <= list1[0]:
        return [list2[0]] + merge(list1, list2[1:])
        
list1 = [3, 7, 9]
list2 = [1, 2, 5, 10]
mergedList = merge(list1,list2)
print(list1, list2, mergedList)