It my be noted that the function considered in the example was completely specified, i.e., there was no don't care terms. If the function is incompletely specified then we follow the same procedure discussed above (for completely specified functions), however, we drop the mean terms that contain only don't care minterms. Specifically, a product term is a prime implicant of an incompletely specified function if it is a prime implicant of the function and contains at least one minterm which is not don't care.

Now we will consider the following example, which illustrates tabular method for incompletely specified functions.

Consider the function written in SOP form

The function in minterm canonical form is as follows

.

The table for consensus of the SOP is shown in Table 5.

The prime implicates are and . However, we do not consider as prime implicate because it comprises only don't care terms.

It may be noted that in case of merging, if both the terms in consensus are don't care, then the new term is also marked don't care. In this example, the term in second column is marked don't care because both the terms in consensus are don't cares.