5.7 EXAMPLES OF MINIMUM FUNCTION EXTRACTION 209
where the 2
n
M
i
in Eq. (5.19) represent maxterms read in maxterm code, and the f
i
repre-
sent their respective coefficients whose values derive from the binary set {0, 1}. The 2
n
M
i
maxterms are mutually disjoint since only one maxterm can be inactive (logic 0) for the
same values of inputs. For this reason it is permissible to interchange the AND and EQV
operators in Eq. (5.19). Thus, Eq. (5.19) expresses the transformation of a POS expres-
sion to an EQV-product-of-sums (EQPOS) expression. Note that if all f
i
are logic 0, then
F
n
= 0.
Setting x
i
=¯x
i
0 eliminates all x
i
from Eq. (5.19), resulting in a negative polarity
expression for the function F
n
, which is simplified by multiple applications of the EQV
form ...