Extrapolated alternating direction implicit methods for solving the biharmonic equation in three space variables Apostolos Hadjidimos (1971) Δελτίο της Ελληνικής Μαθηματικής Εταιρίας
Extrapolation Applied to Certain Discretization Methods Solving the Initial Value Problem for Hyperbolic Differential Equations. W. Hackbusch (1977) Numerische Mathematik