We investigate a class QNC(ADD) that is QNC with gates for addition of two binary numbers, where QNC is a class consisting of quantum operations computed by constant-depth quantum circuits. We show that QNC(ADD) = QAC(PAR) = QAC(MUL), where QAC(PAR) and QAC(MUL) are QAC with gates for parity and multiplication respectively, and where QAC is QNC with Toffoli gates of arbitrary fan-in. In the cla...