Generalizations of Euler’s $$\varphi $$-function with respect to systems of polynomials of several variables

Abstract We introduce a new generalization of Euler’s $$\varphi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>φ</mml:mi> </mml:math> -function associated with a system of polynomials of several variables. We reprove by a short direct approach certain known related identities, and study some other special cases that do not appear in the literature. We also discuss the unitary analogues of these functions.