UNIX for Dummies Questions & Answers

I have a question

I have like 19 different list which contains the name of the server but what I need is just unique ones.

First thing I need to do is just make a unique list within the list itself
i.e. delete anything that is repeated inside the list
like for example

in list1
i have
a
b
c
d
e
a
c
f
g
h


so i just need is a b c d e f g h i mean unique values which is easier anyone can do it i guess.
For the first list its ok

Like that i have 19 liist and i have to do that the same thing which is ok not that hard

the problem is now,

there should not be anything repeating in any one of those list
i.e. if something is there in the first list means that should not be in 2nd list and so on. so that means
for the first list its ok i dont need to do anything as it is after deleting the duplicates

second list I have to compare with the first list and delete if anything from the first list

third list i have to compare with first and second list and anything present in first or second list I have to delete from third list and so on upto 19 list

Plz can anyone suggest me how can i do that

let me know if anything confusing

just i want is not repeated in any one of those 19 list i hope thats pretty much clear

Thanks In advance
its serious problem im having

Pipe it through sort -u