The following steps are a useful formal approach to combinational problems:

- Devise a truth table of the independent input variables and the resulting output quantities.
- Write Boolean algebra statements that describe the truth table.
- Reduce the Boolean algebra.
- Mechanize the Boolean statements using the appropriate logic gates.

Consider the truth table that defines the OR gate. Using the lines in this table that yield a true result gives.

Since *Q* is a two-state variable all other input state combinations
must yield a false.
If the truth table had more than a single output result, each such
result would require a separate equation.
An alternative is to write an expression for the false condition.

Tue Jul 13 16:55:15 EDT 1999