In a K-map, I know block consists entirely of don't cares and is not part of a bigger block is considered as Prime implicant. For ex-The one in red in the given figure- enter image description here

But I am not able to figure out the reason behind it. As that Prime implicant is of no use then why to consider it even as prime implicant?

  • 1
    \$\begingroup\$ Give an example \$\endgroup\$
    – Voltage Spike
    Aug 15, 2018 at 18:25
  • \$\begingroup\$ Updated it in question. \$\endgroup\$ Aug 16, 2018 at 9:05

1 Answer 1


Prime implicants are the minimal parts of a boolean equation that can represent your function. Since you can represent part of your function with the don't cares, they do count as prime implicants even if every part of the implicant is a don't care.


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