In digital logic reduction using a Karnaugh map, a prime implicant is the largest possible rectangular group of 1s. It becomes an essential prime implicant if it contains at least one 1 that is not shared with any other group. These terms must be included in the final simplified Boolean expression, as omitting them would leave a valid input state unaccounted for.
Circle the corners first, because that gives us an essential prime implicant that covers the zero-zero state.
Related terms
Prime implicant
The largest possible grouping of ones or zeros in a Karnaugh map used for logic minimization.
Non-essential prime implicant
A grouped logic term in a Karnaugh map whose outputs are entirely covered by other groupings.
Combinational logic
A type of digital logic where outputs are determined entirely by the present combination of inputs.