In the truth table above, there are two inputs: input A and input B. There are four possible
combinations of these inputs (22 = 4). The input columns are vertical and are set up like
the binary numbers which equal 0, 1, 2, and 3. Notice, in the truth table above, the input
combinations and the vertical columns are set (from top to bottom) like the binary
numbers 00, 01, 10, and 11. A truth table for three inputs has eight possible input
combinations (23 = 8), and the vertical columns are set up from 000 through 111, as shown
How many possible combinations of inputs are there for any four-input logic diagram?