The next thing we need to know is whether the display requires a 0 or a 1 on each segment input to light that segment. Both types of displays exist. The design specification must also indicate which of the alternative displays for 6, 7, and 9 should be used, or state that it doesn’t matter. Finally, we must decide what to do about the inputs that do not correspond to a decimal digit (1010, 1011,... , 1111).