a => 1:b => 2:c => 3:
a => 1:b => 2:c => 3:
a => 1:b => 2:c => 3:
a => 2:b => 2:c => 3:
a => 2:b => 1:c => 3:

unique
a => 2:b => 2:c => 3:
a => 1:b => 2:c => 3:
a => 2:b => 1:c => 3: