Realize (a'b'c'+a'bc+ab'c+abc') using only 2-input x-nor gates.
I've taken a shot at this, however I'm only able to but it into more or gates.
a'(b'c'+bc)+a(b'c+bc')
a'[(b'+c)(b+c')]+a[(b'+c')(b+c)]
a'(b'c+bc')+a(b'c'+bc)
That's where I got, however it's really no simpler and I doubt is...