root:
  li:{} [root] FIRST li:{empty} LAST li:{non-empty}
   li:{empty} 
   li:{non-empty} FIRST te:{key1} LAST te:{key2}
    te:{key1} {val1}
    te:{key2} {val2}
first list:
  li:{empty} 
second list:
  li:{non-empty} FIRST te:{key1} LAST te:{key2}
   te:{key1} {val1}
   te:{key2} {val2}
nth 0:
  te:{key1} {val1}
nth 1:
  te:{key2} {val2}
nth 2:
  * node is NULL *
nth -1:
  * node is NULL *
