de morgan's theorems
de morgan's theorems for two variables are
for 
variables, the complement of any expression can be obtained by replacing eaach variable and element with its complement and, at the same time, interchanging the OR and AND operations, that is,
eq-gen-demorgan is known as the general de morgan's theorem
[cite:@kohavi_switching_2010 chapter 3.1 switching algebra]
for variables, the complement of any expression can be obtained by replacing eaach variable and element with its complement and, at the same time, interchanging the OR and AND operations, that is,eq-gen-demorgan is known as the general de morgan's theorem[cite:@kohavi_switching_2010 chapter 3.1 switching algebra]
