list

x = L.head
while (x.next =/= NULL) do
        if (x.prev.key == x.key)
		then DELETE(L, x.prev)
x = x.next



DELETE(L, x)
if x.prev =/= NULL
then x.prev.next = x.next
else L.head = x.next

if x.next =/= NULL
then x.next.prev = x.prev