Add De Morgan's Laws

Actually, the solution now doesn't use Morgan's Laws at all... It's much simpler, but I'm still unsure if in the case of MATH220, the truth table isn't what is intended. In any case, we have both now :)

Beauty! And Rightarrow or rightarrow may not be that big of a deal after all. We can still change it if people start commenting that it's confusing.

deal!