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Linear Differential Transformations of the Second Order. The English University Press, London 1971.
MR 0463539
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To the Definition of the Global Transformation in 2-dimensional Linear Spaces of Continuous Functions. ACTA UPO Vol.88, 1987, in print.
Zbl 0715.34012
[3] Laitochová D.:
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Zbl 0692.46019
[4] Stach K.:
Die vollständigen Kummerschen Transformationen zweidimensionaler Räume von stetigen Functionen. Arch.Math.Brno, T3 1967, 117-138.
MR 0239168