BoredQuantities   If the variable X is added to the variable Y the sum is the quantity of X and Y X cannot equal to Y ever So in theory if two different variables are added the sum outcome of the eqation will be the quantity of both variables and will NEVER equal to one of the two variables  You say X  Y  Z  Z never Equals X Z never Equals Y  Its faulty X   Y   So X  Y  Z   therefore Z  Y  hehe  C What you meant to say is  If any two variables X Y XY   are added the sum will never equal any one of the two variables  D But what if we take a person with  different ancestries In theory if one has  different ancestries they are never just one of the ancestries however you would qualify such a statement  So X  Y  Z  A A can never equal X Y or Z  Of course here wed have to add the condition that X Y and Z must be   Whereas in Example C the variables just cannot equal