Direct Factors of Polynomial Rings over Finite Fields. - John Knopfmacher (J. Comb. Theory A, 1985)

Counting irreducible factors of polynomials over a finite field. - Arnold Knopfmacher; John Knopfmacher (Discret. Math., 1993)

Arithmetical Semigroups Related to Trees and Polyhedra. - Arnold Knopfmacher; John Knopfmacher (J. Comb. Theory A, 1999)