To find the simplest sum of product form of $f(A,B,C,D)={\displaystyle \underset{?}{\overset{?}{}}}(12,13,14,15)$ with don't

care conditions $d(A,B,C,D)={\displaystyle \underset{?}{\overset{?}{}}}(8,9,10,11)$ we consider

a$.m9=m10=1,m8=m11=0$

b$.m9=m11=1,m8=m10=0$

c$.mg=m11=m8=m10=1$

d$.mg=m11=m8=m10=0$