What are the four steps of the sum-of-products algorithm?
1. Add subexpressions, multiply subexpressions, add gates, repeat as necessary
2. Compare for equality, subexpression construction using AND and NOT gates, subexpression addition using OR gates, subexpression multiplication
3. Truth table construction, subexpression construction using AND and NOT gates, subexpression combination using OR gates, circuit diagram production
4. Select input column, add inputs, multiply inputs, select output column