Minification of truth table with many don't-care fields

[Simsso]

Issue Description

For the appended input the output is correct, but not fully minified. Right now it seems like the bug is within the Quine-McCluskey implementation, more specifically in the way it deals with don't-care fields (X) and the number of different columns between two rows that of which at least one contains a don't-care field.

E.g. the two rows

I7 I6 I5 I4 I3 I2 I1 I0 O1
0 1 X X X X X X 1
1 X X X X X X X 1

should result in I7 + I6 not in !I7 * I6 + I7.

Input

I7 I6 I5 I4 I3 I2 I1 I0 O1
0 0 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 1 X 0
0 0 0 0 0 1 X X 1
0 0 0 0 1 X X X 1
0 0 0 1 X X X X 0
0 0 1 X X X X X 0
0 1 X X X X X X 1
1 X X X X X X X 1

Output

Current Version

O1 = !I7 * !I6 * !I5 * !I4 * !I3 * I2 + !I7 * !I6 * !I5 * !I4 * I3 + !I7 * I6 + I7

Table format

I7 I6 I5 I4 I3 I2 I1 I0 O1
0 0 0 0 0 1 X X 1
0 0 0 0 1 X X X 1
0 1 X X X X X X 1
1 X X X X X X X 1

Desired

O1 = I7 + I6 + !I5 * !I4 * I3 + !I5 * !I4 * I2