A Boundary value Problem for Equations of mixed type John Papadakis (1973) Δελτίο της Ελληνικής Μαθηματικής Εταιρίας
A class of boundary problems for extremal surfaces of mixed type in Minkowski 3-space. Chaohao Gu (1988) Journal für die reine und angewandte Mathematik
A Convergent Finite Elemet Formulation for Transonic Flow. Harald Berger (1989/1990) Numerische Mathematik
A Finite Element Method for a Boundary Value Problem of Mixed Type. A.K. Aziz, M. Schneider, Houde Han (1984) Numerische Mathematik
A Finite Element Method for the Tricomi Problem. A.K. Aziz, M. Schneider, A. Werschulz (1980) Numerische Mathematik
Approximation of Tricomi Problem with Neumann Boundary Condition. M. Vanninathan, G.D. Veerappa Gowda (1984) Numerische Mathematik