A function is self dual if it is equal to its dual (A dual function is obtained by interchanging. and +).
For self-dual functions,
1. Number of min terms equals number of max terms
2. Function should not contain two complementary minterms - whose sum equals 2
n - 1, where n is the number of variables.
so here (0,7) (1,6) (2,5) (3,4) are complementary terms so in self-dual we can select any one of them but not both.
possibility because say from
we can pick anyone in minterm but not both.
NOTE:here i have taken only one of the complementary term for min term from the sets.
so remaining numbers will go to MAXTERMS
For above example, 2
4 = 16 self dual functions are possible
so if we have N variables, total Minterms possible is 2
nthen half of them we selected so
.
and now we have 2 choices for every pair for being selected.
so total such choices