De Morgan's Laws
Given a switching function f(X,Y,...), to obtain its complement f':
(1) Change all + operations to •.
(2) Change all • operations to +.
(3) Complement each variable
e.g. f'(X,Y,Z) = X + X•Y'•Z'•(X•Y + Z•Y')
f(X,Y,Z) = X'•(X'+Y+Z) + (X'+Y')•(Z'+Y)