“…This is shown using a well-known "contraction" argument (see examples in [4] and [11]). The idea is to construct a primitive solution modulo p a+b in N = (Φ(R, k, a) + 1) · (Φ(R, k, b) + 1) variables as follows: First divide the left hand side of ( * ) into Φ(R, k, a) + 1 subsystems of diagonal forms, each in Φ(R, k, b) + 1 variables, and solve each system primitively modulo p b .…”