if a,b,c are arbitraty sets, shows that
[(a u B ) - (b U C) ]intersect ( A u C) ' = null
my steps
[ (a u b) intersect ( b u c )' ]intersect (A u c )'
[ ( a u b ) intersect ( b' intersect c') ] intersect ( A u c)'
[ ( a u b ) intersect b' ( a u b ) intersect c' ] intersect ( a u c )'
STUCK at here. dont knw to continue
edit*[(a u B ) - (b U C) ]intersect ( A u C) ' = null <---------got [ ] inside