So I'm doing some homework and trying to simplify $(x'+y)'(x+y)'$. So far these are the steps I've completed, but I'm not 100% sure that they're appropriate.
$(x'+y)'(x+y)' = (x'+y)'(x’y’)$
$(x'+y)'(x’y’) = (x’’+ y’)(x’y’)$
$(x’’+y’)(x’y’) = (x+y’)(x’y’)$
I'm unsure of what to do after this step (or if I've made any actual mistakes)