Checking Relations using the
Boole-Shannon Principle
lRelations hold iff they hold for any substitution of 0 and 1 for the variables (uniformly throughout the expression)

lTherefore, a relation holds if, choosing any variable V, it holds for V = 0 and for V = 1.

lBut substituting 0 or 1 for a variable often yields simplifications that make the relation obvious.