Two-level circuits
A Sum-of-Products expression is of the form f = X + Y + A + B + …, where X, Y, A, B, … contain only the AND operator and literals.
A literal is an occurrence of an input variable or its complement.
A Product-of-Sums expression is of the form g = XYAB…, where X, Y, A, B, … contain only the OR operator and literals