A method is presented to pick out candidates for completely integrable nonlinear partial differential equations among those in the same form but with their coefﬁcients being different in value. This method is based on the singularity analysis of Weiss et al. As an example, the ﬁfth order KdV type equations are investigated. Investigations of various forms of nonlinear partial differential equations by this method will be of some help to the systematic study of the complete integrability.
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