Simplification of Switching Functions Using K-maps
K-map cells that are physically adjacent are also logically adjacent. Also, cells on an edge of a K-map are logically adjacent to cells on the opposite edge of the map.
If two logically adjacent cells both contain logical 1s, the two cells can be combined to eliminate the variable that has value 1 in one cell’s label and value 0 in the other.
This is equivalent to the algebraic operation, aP + a?P =P where P is a product term not containing a or a?.
Example -- f(A,B,C,D) = ?m(1,2,4,6,9)