Question: How do I ignore terms containing certain combinations of functions (higher order terms) in a differential equation?

I need to simplify a differential equation by ignoring higher order terms. The terms are of the following form:


Here beta, zeta and theta are hinge deflections for a helicopter blade and thus can be assumed to be small. Everything other than delta__3 is a function of time, _dot represents a derivative wrt time. Higher order terms, such as those containing betan, zetan, thetan where n > 1, and terms containing combinations of the hinge deflections, i.e. betaj.zetak, betaj.thetak or zetaj.thetak where j,k >= 1 need to be neglected. Since beta, zeta and theta are functions of time, and the equation contains derivatives, maple functions like 'degree' and 'match' don't seem to work. Also, the solution suggested over here does not seem to be suitable for this problem, since my equation is very long (~70 pages) and the various derivatives appearing in it are not known.

Thanks in advance!



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