So we have proved that A + AB is equivalent to A+ B. 1.3 DeMorgan's Theorems Another very useful class of boolean algebra equivalences is given by DeMorgan's Theorems, which give us the power to break a negation of a product or a negation of a sum into smaller pieces. Here are the two forms: Comment Equivalence Name AB - A+B NAND to Negative-OR A+ B = A B NOR to Negative-AND So now write a two column proof that starts with an application of one of DeMorgan's theorems on the given left hand side to prove the following equivalence: A + BC + AB - AB