The principal disjunctive normal form consists of the sum of the minimum terms, and the true value of the propositional formula obtained by assigning the minimum terms contained in the principal disjunctive normal form simplified by the propositional formula should be 1.

The principal conjunctive normal form consists of the product of the maximum term, and the subscript corresponding to the maximum term contained in the equivalent principal conjunctive normal form of the propositional formula should be such that the corresponding assignment leads to the truth value of the propositional formula being 0.

So, suppose there are three propositional elements, and the subscripts of the minimum term and the maximum term are 0-7 respectively. If the principal disjunctive normal form of a propositional element is expressed as m 1 or m3 or m5, then its principal conjunctive normal form should be M0 and M2 and M4 and m6 and M7.

In other words, subscripts are the complement of the minimum set of subscripts.