On monotonicity preserving linear extrapolation sequences. - Gerhard Opfer (Computing, 1970)

Interpolating Cubic Splines. - Gerhard Opfer; Gary D. Knott (J. Approx. Theory, 2001)

A note on hyperbolic transformations. - Dása Janovská; Gerhard Opfer (Numer. Linear Algebra Appl., 2001)

The classification and the computation of the zeros of quaternionic, two-sided polynomials. - Drahoslava Janovská; Gerhard Opfer (Numerische Mathematik, 2010)

A Note on the Computation of All Zeros of Simple Quaternionic Polynomials. - Drahoslava Janovská; Gerhard Opfer (SIAM J. Numer. Anal., 2010)