An Incompletely specified function is a Boolean function that only define output values for a subset of its inputs. For outputs that are not specified, the inputs are treated as don't care values. Incompletely specified functions often make no guarantees as to the unspecified output whatsoever.

Overview

In many situations when working with combinational circuits, some combinations of inputs cannot occur or should not occur under normal working conditions. For those combinations the output can be disregarded allowing for possibly further logic minimization.