given f = Σ(5,6,13) and f1 - Σ(0,1,2,3,5,6,8,9,10,11,13)
and f = f1 . f2 '
and if we want f = Σ(5,6,13)
Σ(5,6,13) = Σ(0,1,2,3,5,6,8,9,10,11,13) . { Σ(5,6,13) + d(max term of f1)
Σ(5,6,13) = Σ(0,1,2,3,5,6,8,9,10,11,13) . { Σ(5,6,13) + d(4,7,12,14,15) }
so f2 ' = Σ(5,6,13) + d(4,7,12,14,15)
then f2 = Σ(0,1,2,3,8,9,10,11) + d(4,7,12,14,15)
(on compliment don't care do not change)
So f2 = B'