A, B, C, D
AB, AC, AD, BC, BD, CD
ABC, ABD, ACD, BCD
ABCD

##</code><code>##

ABCD
    ABC
        AB
            A
            B
        AC
            C
        BC
    ABD
        AD
            D
        BD
    ACD
        CD
    BCD         

##</code><code>##

Set1:  A,B,C,D
Set2:  A,B,C,E
set3:  A,B,C,F,G