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Published online by Cambridge University Press: 20 November 2018
We consider a system of differential equations of second order given by
1
(' = d/dt) where P and Q have continuous first partial derivatives with respect to x and y in some open and simply connected set R containing O = (0, 0) which we assume to be the only singular point in R. In fact, let R be the whole plane; for if not then the following discussion can be modified.