*1. De Morgan’ theorem 1:**
When the OR sum of two variables is inverted, this is the same as inverting each variable individually and then ANDing these inverted variables.
(X + Y)’ = X’. Y’
*2. De Morgan’ theorem 2:**
When the AND product of two variables is inverted, this is the same as inverting each variable individually and then ORing them.
(X.Y)’ = X’ + Y’
