as long as there is 'A' & 'B'
'A' can look to 'B' for difference
and 'B' can look to 'A' for difference
but if 'A' = 'B' there might as well just be 'A'
or just 'B'
difference must be searched for
......no this is wrong
if 'A' knows 'B' = 'A' and 'B' knows 'A' = 'B'
they both become 'C'
and they both then see 'A' and 'B'