c:\test>600418.pl
This input

        0 0 1 1 0
        1 0 1 1 1
        0 1 0 1 0
        1 1 0 0 1
        0 1 1 1 0

Inverted looks like this

        0 : 01010
        1 : 00111
        2 : 11001
        3 : 11101
        4 : 01010

This subset can be removed from the main group:

        0 : 01010
        4 : 01010

c:\test>600418.pl
This input

        0 0 0 1 1 0 0 0
        0 1 0 1 1 1 1 0
        1 0 1 0 1 0 1 1
        1 1 1 0 0 1 1 1
        1 0 1 1 1 0 0 1

Inverted looks like this

        0 : 00111
        1 : 01010
        2 : 00111
        3 : 11001
        4 : 11101
        5 : 01010
        6 : 01110
        7 : 00111

This subset can be removed from the main group:

        1 : 01010
        5 : 01010

This subset can be removed from the main group:

        0 : 00111
        2 : 00111
        7 : 00111